Types of natural stone: Categories and features
Find out here the types of natural stone you can use for your home decoration project, but also the categories and features.
The main natural rocks
Limestone
Marble
Slate
Travertine
Granite
Elements of petrology
What is a rock?
How do you classify rocks?
Types of rocks from a genetic point of view
Magmatic rocks
Metamorphic rocks
Sedimentary rocks
Description of rocks: What do you need to know about them?
Granite
Basalt
Marble
Slate
Limestone/Travertine
Sandstone
The main natural stones
LIMESTONE
Limestone is a sedimentary stone consisting mainly of calcite minerals. In some situations, calcium carbonate can be directly precipitated from sea water, but usually it forms from the fossils of sea creatures. These shells can be intact or broken into small particles. There are many types of limestone, the differences consisting of color, porosity and durability. Limestone is resistant to moisture, but is sensitive to acidic solutions. Due to its porosity, this stone must be protected from acidic substances and water by sealing its surface.
MARBLE
Marble is a metamorphic stone. Similar to travertine, marble is a variety of limestone, but there are many differences between these two natural stones. Due to the fact that is a saltwater rock, marble quarries are close to the sea. As a result, marble is generally associated with the ancient cultures of Rome and Greece. There are, however, marble quarries far from the seashore, such as those in the U.S. or Germany. It has a higher density than travertine and has a wide color variation. Besides white marble, which is the most popular, you have also blue, green, black or other colors of marble. One of the most famous marble buildings is the Taj Mahal Palace in India.
Main physical properties of marble:
Physical features of marble include hardness, density, compression, etc. Most marbles (with very few exceptions) have the following features:
Hardness: 3 - 4 on the Mohs scale
Density: 2.55 - 2.7 Kg/cm3
Compressive strength: 70 - 140 N/mm2
Flexural strength:12 - 18 N/mm2
Water absorption: less than 0.5%
Porosity: very low
In terms of chemical properties, marbles are crystalline rocks consisting mainly of calcite, dolomite or serpentine, along with other minor components that are variable.
SLATE
Slate is a metamorphic rock shaped and hardened at high temperatures under the pressure of earth's crust, as a hard and durable stone. Even though slate is usually available in dark colors, it has a wide range of shades. The color of slate depends very much on the quarry location: red, cream, ochre, green, gray and black. Depending very much on its quarried place, the slate has a fine grain size, different textures and even different patterns. You will not find 2 identical slate tiles. It will not stain, nor absorb moisture. It is necessary to seal its surface to maintain its beautiful look and extended lifetime.
Main physical properties of slate:
Apparent average density: 2.6 - 2.8 t/m3 (slate is a compact rock)
Water absorption: 0.1 - 0.6 % (very low; slate undergoes a significant dehydration by compaction and has a low porosity; nevertheless, slate needs surface sealing)
Hardness on the MOHS scale: 6-7 (slate is a quite hard rock; diamond is considered the hardest, with a value of 10)
Porosity: low (due to significant compaction during formation)
Insulator: yes (electric)
Color: wide color range, according to mineralogic composition (from black, when containing organic material, to red, when containing iron oxides); black, gray, green, variegated (the last is the most popular), rarely light colors.
Mineralogic composition: frequently composed of limestone and clay minerals (muscovite or illite) to which other minerals (biotite, chlorite, hematite) are added in different proportions
Organic composition: black slates contain animal and plant organic matter; fossils sometimes occur due to the low degree of metamorphism.
TRAVERTINE
Travertine is a natural stone from the limestone family. It consists of calcium carbonate and is often found in the form of sediments near hot springs. Travertine is a very porous natural stone and sensitive in contact with acidic and citrus substances as well as to cleaning. It is recommended to seal its surface to protect it against accidental staining. The Rome Colosseum is one of the most famous buildings made mostly of travertine. Its name comes from the Italian word "travertino", derived from the ancient Roman name Tibur (now Tivoli), a town near Rome with a quarry where travertine has been exploited since ancient times.
GRANITE
Granite is a very hard, crystalline, magmatic rock, with crystals size starting from a few millimeters. It is shaped deep within Earth’s crust and consist mainly of quartz, feldspar and dark minerals. In terms of color, granite tiles are usually gray, white, black, pink, blue, yellow or red. There are granite tiles very similar to marble, however, granite is more resistant when subjected to scratches, acids and fire. Because of its features, this natural stone has been used as building material for thousands of years. The word comes from the Latin "granum" which means grain.
Main physical properties of granite:
the average density: 2,65 – 2,75 g/cm3, values requiring very low permeability and water absorption (0,1 to 0,6 %);
- compressive strength – approximately 200 MPa (megapascals) or 140 - 210 N/mm2;
- the melting temperature: between 1215 and 1260 °C;
- hardness on the Mohs scale: 6 – 7.
Notions of petrology
Because rocks and minerals have significant economic and practical importance, their study established itself as a necessity a long time ago. Thus, originated a new science, with many areas of approach – Geology. Among the branches of Geology is Petrology, a complex and extended domain of analysis of rocks.
Petrology is a branch of geology that deals with the petrogenetic and petrographic study of rocks:
- petrogenesis is an area of petrology that addresses the complex problems of the genesis of magmatic, metamorphic and sedimentary rocks and the sequence of genetic processes that led to their formation;
- petrography is a discipline of petrology which aims at the inventory, classification and description of rocks in terms of mineralogic constitution, structure and texture.
Petrology, in turn, is divided according to the field of the earth's crust that it studies into:
- endogenous petrology (includes the study of magmatic and metamorphic rocks);
- sedimentary petrology (study of rocks formed in sedimentation basins on the earth's surface);
- the petrology of rocks in deep areas of the crust.
What is rock?
Rock is a heterogeneous mineral aggregate, usually poly mineral (it can also be mono mineral), formed by natural processes inside the earth's crust or on its surface, characterized by a well-defined mineral composition, structure and texture. The criteria used in the general classifications of rocks refer to the field of formation relative to the topographic surface, the genetic processes that control their formation and the chemical-mineral composition.
How do you classify rocks?
Depending on the field of formation reported to the topographic surface are distinguished:
- endogenous rocks are formed under the control of endogenous processes, from inside the earth's crust (magmatic and metamorphic) Examples: granite, basalt, andesite, marble, slate
- exogenous rocks are formed in sedimentation basins on the earth's surface under the control of exogenous processes. Examples: limestone, dolomite, travertines, sandstones, clays.
From a genetic point of view, depending on the main types of processes leading to the formation of mineral aggregates, they differ:
- magmatic rocks - are aggregated usually poly mineral, with silica in composition, formed by solidified magma within the crust (intrusive rocks) or on its surface (extrusive or volcanic rocks);
- metamorphic rocks - are poly mineral or mono mineral aggregates formed by solid recrystallization (= blastesis) of pre-existing rocks, under the action of dynamic factors (predominantly pressure), thermal (predominant temperature) or dynamo thermal (pressure and temperature);
- sedimentary rocks - are aggregates that form in sedimentation basins on the ground, underwater or subaerial surface, under the action of exogenous processes: physical (disaggregation, transport, accumulation, etc.), chemical (chemical precipitation, alteration, etc.) and biotics (biochemicals, bioaccumulation, etc.).
Types of rocks from a genetic point of view
Magmatic rocks
Magmatic rocks, in a broad sense, includes both rocks shaped by solidified magma in depth and the lavas over the surface.
Magma is a natural multi-component system, stable at temperatures above 6500 °C, consisting of a liquid phase (assimilated with the composition of a silicate melt) a gaseous phase (made up of volatile elements) and a solid phase. Magmatic rocks (also called plutonium or depth) are shaped from magma upon cooling.
The most common magmas are silica (with SiO2 over 30%), but in nature they can be found in reduced proportions and carbonic, sulfuric and oxidic magma.
Silicic magma is classified according to the silica content in:
- acid magma, includes over 63% SiO2 (percentage by weight);
- neutral magma, with 52% and 63% SiO2;
- basic magma below 52% SiO2. In the basic magma a large amount of volatile substances is dissolved, which gives them a greater fluidity compared to acidic ones.
Lava is a magma that reaches the surface and overflows losing some of the volatile substances. Volcanic rocks (extrusive) are born from the lava. Similar to magma, they can be acidic, neutral or basic. Basic lavas are hot and more fluid and acidic ones colder and more viscous.
Following the solidification of magma and lavas, plutonic and volcanic rocks are formed consisting of crystallized or amorphous solid mineral phases (vitreous-glass).
Classification of magmatic rocks
The classification of magmatic and volcanic rocks is based on several criteria. The most common refers to:
a. the field of solidification in relation to the terrestrial topographic surface;
b. chemical composition (acidity – basicity, depending on the amount of silica);
c. rock structure (degree of crystallinity, i.e. the ratio of crystallized and uncrystallized volume in the mass of the rock; size of crystals);
d. mineralogic composition (after the percentage participation of quartz, potassium feldspar, plagioclase and feldspathoid).
A. Depending on the field of rock solidification in relation to the topographic surface, it is classified in:
- plutonic rocks (magmatic, intrusive) – solidified under the topographic surface;
- volcanic rocks (extrusive) – solidified on the surface.
The plutonium rocks are characteristic of the phaneritic and holocrystalline structures, because they were solidified deep within the earth crust, where the variation in temperature and pressure was slow, which allowed the complete crystallization of the magma and a longer physical time for the growth of crystals in relation to the surface.
In contrast, volcanic rocks formed at/or close to the surface are characteristic of hyaline, aphanitic or porphyritic structures, characteristic of a much faster cooling in relation to the underground domain.
Each intrusive rock has a surface equivalent (extrusive) similar by chemical composition, but different in the crystals look.
Intrusive rocks Extrusive rock
Granite Rhyolite
Granodiorite Dacite
Diorite Andesite
Syenite Trachyte
Gabbro Basalt
*acidity rises from gabbro to granite and from basalt to rhyolite respectively
B. In terms of chemical composition and according to the SiO2 content, magmatic rocks are classified into:
- acid: with above 63 % SiO2 content, in which quartz is associated with minerals such as feldspars, micelles, amphiboles, etc., (e.g. granite-granodiorite and rhyolite-dacite);
- intermediate: with SiO2 content between 52 % and 63 % in which free quartz is missing or found in small quantities, instead increases the percentage of ferro-Magnesian silicates (e.g. andesite);
- basic: in which the content in SiO2 is 45 % - 52 %, without quartz, but rich in ferromagnesian silicates (e.g. basalt);
- ultrabasic: consisting of 30-45% SiO2 content and the prevalence of olivine, as is the case with peridotite. They are known in the continental domain only in the deep areas of the crust, at the crust contact with the asthenosphere and in the field of oceanic rifts.
c. By structure, magmatic rocks are classified as follows:
c.1. By degree of crystallinity, especially the proportion of glass:
- holocrystalline rocks have all the fully crystallized mass, such as plutonium rocks (granites, gabbro, etc.);
- hypo crystalline rocks made up of both crystals and glass, as in the case of extrusive rocks (andesites, rhyolites, etc.);
- hyaline rocks (vitreous = glassy) that have the entire glassy mass, without crystals, such as volcanic bottles, obsidian and pumice stone.
c.2. By the absolute size of the crystals:
- phaneritic rocks with crystals visible to the naked eye, greater than 0,2 mm;
- aphanitic rocks with crystals invisible to the naked eye, less than 0,2 mm.
Metamorphic rocks
As a result of the lithosphere dynamics (the dynamics of the earth's crust), some of the rock volumes get to be, under pressure conditions and temperature, significantly different compared to their condition of origin, which causes a series of transformations in their solid state, thus giving rise to another category of rocks, known as metamorphic rocks.
The totality of solid transformations by which pre-existing rocks tend to adapt to new pressure and temperature conditions is called metamorphism. This process results in the metamorphic rocks.
Metamorphism consists in the transformation into a solid state of a pre-existing rock (protolith), into a new rock (metamorphite). Metamorphy differs from protolith by petrographic structure, mineralogic composition and chemical composition. The protolith can be represented by any type of pre-existing rock in the bark: magmatic, sedimentary or even metamorphic.
The effects of metamorphic processes are as follows:
- changing the petrographic structure either by rearranging the crystals of the protolith in space or by changing the shape and dimensions of the crystals;
- change of mineralogic composition of the protolith, global chemistry constantly maintaining the protolith and metamorphite;
- change in the global chemical composition of protolith (rarely).
Deep within the earth’s crust, as the depth increases, the temperature, pressure (lithostatic and stress) and fluid composition change. These parameters are the main control factors of metamorphism.
Temperature
It is an essential metamorphism factor and it increases as the depth increases, which makes rocks to heat up. Working temperatures for metamorphic processes belongs to the range 200°C - 1000°C. Temperatures below 200°C characterize the areas in which sediment diagenesis occurs (transformation of sediments into sedimentary rocks), from 200°C to the first transformations into clays, and at more than 1000°C the melting of anhydrous rocks (the anataxis process) begins. Depending on the temperature value between the two variability limits, four steps (degrees) of metamorphism can be established:
- low (anchimetamorphism) between 200 and 400°C – phyllite, slates;
- average between 400°C and 600°C - green schist;
- tall, 600-650°C - amphibole, gneiss, marble;
- very high, 650-700°C close to anatexis called ultra meta morphism.
Pressure
The working temperatures for metamorphism range from values from a few bars (atmospheres), near the Earth's surface, to about 10 Kilobars (10,000 atm), at depths of about 35 km.
In terms of baric conditions, there are three types of metamorphism:
- low, up to 2-4 Kilobars, when weak recrystallizations occur, phyllite form, slates;
- medium, 4-7 Kilobars, with strong recrystallizations, as in amphiboles;
- high and very high pressure, over 7 kilobars, when gneiss, granite-gneiss, etc.
Pressure, as a metamorphism factor, is of 2 categories:
- lithostatic pressure – is one of the factors with general action and constantly increasing with depth, due to increase of weight from the rocks located above. This pressure compresses a body, but it doesn't deform it. Its growth with depth has the effect of altering the density of rocks;
- oriented pressure (stress) - is deformed, because it acts preferentially, in a certain direction. Adaptation to stress is done by the fragmentation of rocks according to the brittle, a process called cataclysm (the resulting rocks are called cataclysms), or by the reorientation of minerals in directions perpendicular to the direction of action of the stress. The re-emergence of minerals in parallel planes, perpendicular to the direction of action of stress, causes the appearance of schistosity, a main diagnostic characteristic of many of the metamorphic rocks. For this reason, for metamorphic rocks, the narrow name of crystalline schists was also used;
Fluids
Fluids act as catalyst for chemical reactions, increasing their speed; represent the vectors that ensure the "migration" of chemical components and are constituted as a chemical and mineralogic transformation factor.
The structure of the metamorphic rocks depends on the degree and type of metamorphism. The appearance and growth of crystals in solid state, by metamorphic recrystallization is called blasthesis and the resulting structures are called crystalloblastic. By the shape of the crystals and the ratio between them are distinguished:
- granoblastic structures represented by granular crystals with almost equal dimensions on the three directions (isometric), e.g. marble;
- lepidoblastic structures (lepidos = fish scale) - deciduous or scaly crystals arranged parallel, similar to fish scales, the common structure at mica schists (crystalline schists with mica);
- nematoblastic structures in which elongated-prismatic crystals are oriented parallel giving the rock a fibrous (amphibolite) appearance;
Texture, i.e. the way of distribution in space of the component minerals, can be:
- schistose, consisting of deciduous minerals arranged according to parallel planes as it is found e.g. in mica schists, slate;
- massive, whose minerals do not have a preferential orientation, e.g. quartzites, marble.
Control factors of metamorphism
In terms of metamorphism intensity, two major categories of rocks can be separated:
- rocks with a low degree of metamorphism, to which the protolith is easily recognizable, which is why the prefix "meta" is added to the name of the original rock; e.g. meta basalt, meta granite, etc.;
- rocks with an advanced degree of metamorphism that does not preserve the petrographic structure of the protolith and sometimes neither its chemistry. Of these metamorphits we mention:
- corneal - isotropic, microgranular, mineralogically diverse metamorphic rocks;
- skarns - usually isotropic rocks composed mainly of calcium silicates;
- marbles - consisting of large calcite crystals;
- quartzites - predominantly quartzite rocks;
- gneiss - schists rocks composed mainly of feldspar and mica;
- mica schists - shale rocks consisting mainly of small and quartz;
- phyllites - fine, schists rocks made up of phyllo silicates;
- green shales - shale rocks formed of bleached and a green mineral (chlorite, epidot);
- amphibolite - shale rocks consisting of hornblende and plagioclase feldspar;
- eclogite - rocks with a high density of more than 3,3 g/cm.
Sedimentary rocks
Exogenous processes and phenomena (from the Earth's surface) cause disaggregation (physical destruction) and alteration (chemical destruction) of rocks that make up the positive forms of the earth's terrain, transport of fragments resulting from the disaggregation of pre-existing rocks and sedimentation (accumulation) in depressive areas, called sedimentation basins. By the accumulation of fragments, the clastic rocks (stones, sands, silts, banks, conglomerates, sandstones, siltites, marls, clays) are born. At the same time, different chemical and biochemical processes are carried out in the basins, forming chemical precipitation rocks (calcium, dolomite, silica, evaporite, etc.) and biotic rocks (organogenic limes, silicolites, coal, oil, gas, etc.).
After the accumulation process, sediments are subjected to physico-chemical transformations of compaction, cementing, etc., known as diagenetic processes. As a result of diagenetic processes, sediments turn into sedimentary rocks.
Due to the diversity of the conditions of formation and the numerous processes that contribute to sedimentary petrogenesis, the classification of sedimentary rocks is complicated. Usually, the criteria for the classification of sedimentary rocks refer to: genetic processes and chemical-mineral composition.
Sedimentary rocks classification
Depending on the predominant genetic processes that control the formation of sedimentary rocks, we distinguish the following types: clastic rocks (epiclastic and pyroclastic), chemical rocks (chemical precipitation and alteration) and biotic rocks (bioconstruction and bioaccumulation).
a. Clastic rocks
a.1. Epiclastic (detritic) rocks were formed as a result of accumulation of clasts (detritus) in sedimentation basins, arising under the action of physico-mechanical processes on pre-existing rocks in the source areas (magmatic, sedimentary, metamorphic). In turn they are classified by the dimensions of the components (classes) and by the degree of consolidation (cementation)
a.2. Pyroclastic rocks are made up of material expelled into the air as a result of explosive volcanic activity and then transported to pools where sedimentation takes place. This category includes bushes and little bushes, pyroclastic agglomerates, volcanic breccias, etc.
B. Biotic (organogenic) rocks are formed either by the accumulation in situ (on the spot) of bioclasts (the remnants of marine organisms, usually shells, or plant detritus, etc.) resulting in bioaccumulation rocks (such as lumasses, peats, coals, etc.), or by the activity of reef organisms (corals, brioches, limestone algae, bacteria, etc.), resulting in bioconstruction rocks (such as reef limestones, stromatolitic limestones, algal limestones, etc.).
Organogenic rocks are classified according to their combustion behavior, in:
- acaustobiolites (non-combustible organogenic rocks) of which reef limestones, diatomitis, radiolarites, spongolites, etc.;
- caustobiolites, representing combustible rocks such as peat, coal, oil and natural gas.
c. Chemical rocks
Chemical precipitation rocks are resulted from the concentration of solutions (oversaturation), which can occur as a result of underwater volcanic emissions, evaporation in arid fields, intense biogenic activity, etc.
Depending on the field in which they were formed, two categories can be outlined:
- continental, formed by precipitation in endocars (precipitation limestones that make up the spleen: stalactites, stalagmites, drapes, etc.), around the springs (limestone, travertines), as well as the cortege of rocks formed by chemical precipitation in continental lakes in water-deficient areas (gypsum, anhydrite, gema salt, etc.);
- marine, resulting from overconcentration in marine basins with restrictive circulation (gypsum, anhydrites, silvine, carnalite, etc.), or in other ways (riding, silicolitis, etc.).
d. Residual rocks are formed as a result of chemical and biochemical alteration and accumulation in situ of hard-soluble minerals (bauxite, laterites, soils).
Chemical-mineral classification
Depending on the chemical-mineral composition, the following types of rocks are distinguished:
A. Carbonatic - represented by biosynthesized rocks (reef lime), and bioaccumulated (chalks, globigerine marl, etc.) or bioclastic rocks (calcarenites, made up of sand-sized bioclasts);
B. Clays - made up of hydrated aluminosilicates: Kaolin, bentonite, various illite clays, montmorillonitic, etc.;
c. Aluminous - formed by residual accumulation (bauxites);
d. Chlorins - resulting from precipitation from oversaturated solutions (gema salt, silvina, et al.);
E. Silica - constituted by the accumulation of tests of silica organisms (diatomite, radiolarites, menilites, jaspers);
F. Sulphate - results from precipitation from marine or lake waters from arid areas (gypsum, anhydrite);
G. Ferruginous - composed mainly of limonite and hematite;
H. Manganese - psilomelan crusts;
J. Phosphate - is formed less often (phosphorites).
Rock description: What do you need to know about this?
GRANITE is an intrusive, textured magmatic rock (the name of the granite derives from the Latin word granum which means cereal, grain) and completely crystallized (holocrystalline). The crystals are visible to the naked eye (phaneritic rock).
GENESIS
Magma that penetrates from the asthenosphere into the earth's crust is initially basic. This magma forms huge bags inside the earth curst called batolites. By melting the rocks in which the batolites are housed, the chemistry of magma changes from basic to acid (increases quartz concentration). The long-term cooling of these acidic magma leads to the appearance of magmatic rocks that have as their main property complete crystallization.
Properties
Chemically, granite is an acidic rock that has in its composition at least 20% quartz (SiO2) and over 65% alkaline feldspars (potassium and sodium silicates). The color of granite varies from white, pink to gray and is imposed by mineralogic composition. The light colors of the rock mass belong to quartz and alkaline feldspars and the darkest ones of biotite (small black variety) and hornblende (variety of silicate in the amphibols group).
Granite appears as a massive rock (without obvious internal structures), with a large and very hard weight, with widespread use in the history of humanity, especially as a construction meter. Its massiveness, heavy weight and hardness are also indicated by exceptional physical properties:
- the average density is between 2,65 – 2,75 g/cm3, values that require very low permeability and water absorption (0,1 – 0,6 %);
- compression resistance is very high – about 200 MPa (megapascals) or 140 - 210 N/mm2;
- the melting temperature of the borders is between 1215 and 1260 °C;
- hardness on the Mohs scale: 6 – 7;
- weather resistance.
Uses
Various uses (through the above-mentioned properties, granite has a wide range of uses: construction material, buildings, bridges, paving, monuments and many other outdoor projects. Inside, polished granite tiles and tiles are used in countertops, tile floors, steps or other practical and decorative uses).
The first uses: construction material for pyramids, temples, mausoleums (because the finishing of borders was, in the ancient times of mankind, an almost impossible thing, only blocks of various sizes were used as exploited from quarries). Modern uses: tombstones, tombstones, sized stone (different thicknesses for different uses), paving stone, kitchen countertops, etc.
Origin
Granite is a rock common on the globe. The countries with the largest production capacity and exports are: China, India, Italy, Brazil, Sweden and Spain.
In Romania, the largest granite quarry is in Iacobdeal in Tulcea County, which has been known since the Turkish occupation. The granite exploited is gray in color, with pink or pink shades with black or blue-green spots (called the granite of Jacobdeal, which next to the granite of Macin, represents the most famous Romanian granite).
BASALT
BASALT is a volcanic rock formed by the rapid cooling of the basic lava (from very deep depths) to the surface or close to the surface of the crust. It is a rock very common on the bottoms of the oceans (it forms the so-called oceanic crust). On the continents appeared only where there were deep fractures, fractures that crossed the continental crust and reached as far as the asthenosphere (famous are the basalt overflows on huge areas of India, Siberia, Brazil, Argentina, eastern Africa, the Hawaiian Islands, Iceland).
The rapid cooling of the basic wash makes the basalt an aphanitic rock (crystals invisible to the naked eye), sometimes hypocrystalline (a glassy mass with crystals trapped in it).
GENESIS
Beneath the earth's crust there is a viscous shell made of basic and ultrabasic magma called asthenosphere. Through deep cracks deep within earth or at the contact between two tectonic plates (tectonic plate = piece of bark that "floats" on the asthenosphere), matter in the asthenosphere can reach the surface where it suddenly cools and forms the basal rock called basalt. Basic lavas, being poor in silica, are very fluid and have the property to flow over very long distances forming real lava fields (Hawaii Islands).
Sudden cooling causes rapid crystallization. Because of this the crystals are not visible to the naked eye (aphanitic rock). The basalt is the most widespread rock on the globe participating in the composition of the oceanic (integral) and continental bark (alongside the predominant granite). In ancient geological times, the deep cracks that affected the continental crust reached as far as the asthenosphere allowing the ascent of the basic magma to the surface. There have been large bursts of basalts that occur today in India, Brazil, Argentina, Siberia.
Sudden cooling close to the surface of the crust of the basic laves leads to the appearance of a structure specific to the basalt – columnar structure (basalt columns with hexagonal profile in most cases; may also be with a pentagonal or quadrilateral profile, but less often). If the sails reach the surface, by solidification give the appearance of overlapping tiles, another structure specific to the basalt (also called basalt in the boards).
Properties
Color: dark gray to black;
Gloss: matte
Hardness: 6 – 7 on the Mohs scale
Average density: 3 g/cm3
Compact: very high (96%)
Porosity: low (it's a waterproof rock)
Durability: withstands physical demands (grinding, breaking, hitting), but it alters very easily in the presence of water and air (because of iron in the composition)
Chemical composition: besides SiO2 (a rock poor in silica 45 – 55%), the basalt contains numerous oxides of magnesium, calcium, iron, titanium and aluminum.
Uses
Various uses (through its properties): building material as blocks, tiles, curbstone or broken stone (buildings, earthworks, foundations, paving, floors in kitchens, bathrooms, hallways), monuments and sculptures. More recently, thermal processing produces the so-called basaltic mineral wool, a good thermal insulator used in houses built of wood. Also, the basalt can be processed by melting into mineral fibers with the appearance of fabric with very varied uses (sound, thermal and fire retardant).
Origin
The basalt is a rock common both on Earth, but also in the other telluric planets of the Solar System (Mercury, Venus, Mars) or natural satellites made up of rock (Moon).
Significant amounts of basalt are found in Canada, USA, Argentina, Brazil, India, South Africa, Russia. In Romania we notice the quarry operations in Racos (Brasov County) and Lucaret (Timis County), as well as the Basalt Columns from Detunatele (landmark in Apuseni Mountains, Alba County),
METAMORPHIC ROCKS
MARBLE
Marble is a metamorphic rock, composed mostly of calcite (calcium carbonate) and obtained by the metamorphosis of limestone. The name comes from the Greek language marmaros = to shine.
From a petrographic point of view, marbles are limes or dolomite with well-developed calcite crystals due to the metamorphic processes to which they have been subjected. The most common colors for marble are: white, gray, gray, black and red, generally due to adjacent impurities (red and yellow from iron oxides, tan from manganese oxides, ash from graphite, etc.), and the veins are shaped by the numerous cracks, later filled with secondary calcite.
GENESIS
Marble is formed from limestone that changes its physical properties under the action of high temperatures and pressures in the earth's crust. These processes cause the limestone to change its texture and appearance, a process called recrystallization. Minerals from impurities give marble a wide variety of colors. The purest marble in terms of calcite is white. The marble containing hematite has reddish color, the one that contains lemonite is yellow and the one that contains serpentine is green. Marbles can also be black, but dark varieties are rare.
Marble cannot be easily separated into sheets of equal size and must be operated with great care. No explosives are used in extraction quarries, because the rock can break. Marble blocks are operated with machines that cut ditches and make holes in the rock. The delimitation of a marble block by the miners is achieved by drawing ditches and holes. The break-up of the block is done with feathers and special machines, the blocks thus obtained are cut with ironworks to the desired shape and size, after which they are finished and polished according to the demands.
So, the marble that we see and admire in different situations is the result of a laborious process of exploitation and processing. The results, however, are amazing. Marble is the most popular natural stone for its physical properties, its multiple uses and for its original appearance.
Properties
The general physical properties of the marble are hardness, density, compression, etc. Most marbles (with very few exceptions) have the following characteristics:
Hardness: 3 - 4 on the Mohs scale
Density: 2.55 - 2.7 Kg/cm3
Compression resistance: 70 - 140 N/mm2
Break mode :12 - 18 N/mm2
Water absorption: less than 0.5%
Porosity: very low
In terms of chemical properties, marbles are crystalline rocks composed mainly of calcite, dolomite or serpentine, along with other minor components that vary from origin to origin.
Uses
Uses: varied (sculpture, building material, tombstones).
Origin
Marble is found in many places on the globe. The most famous marble is Carrara (Italy). Four countries dominate the world's marble production: Italy (the largest producer), China, India and Spain.
The largest marble quarry in Romania is located in the Poiana Rusca Mountains, Caras-Severin County. Ruschita's quarry went into operation in 1884. Marble extracted here (marble of Ruschita) is white with pink shades, blue and grey, compact (98.11%), with small to medium sucrose structure, its special quality being appreciated and abroad (exported to France, Italy, USA, Germany, Austria, Hungary, Egypt) For the construction of Casa Poporului (People's House) – the current Palace of Parliament - were used, along with other materials, 1,000,000 cubic meters of marble.
SLATE (CLAY SCHIST)
Clay rock rich in fine material (clay) and coarser (sand) with advanced degree of compaction. It is a relatively hard rock in the category of metamorphic rocks resulting from the transformation into pressure conditions and relatively high temperature of deposits of clays and fine sands.
Genesis
Fine materials resulting from the erosion of rocks within continents or from eruptions of volcanoes (volcanic ash) are transported by various agents (air, water, glaciers) and deposited in sedimentary basins (seas, oceans, lakes) in the form of sediments (banks). Complex geological processes transform these sedimentary deposits into sedimentary rock called clay. By transforming these clays as a result of the tectonic stress that occurs in the spaces where mountains form, under a weak metamorphism, slate is formed.
The main characteristic of slate is the advanced schistosity, i.e. its quality to break into thin sheets when subjected to certain pressures.
The name comes from the province of Ardes in Ireland from where the first slates were extracted and brought to Europe.
Properties
Apparent average density: 2.6 - 2.8 t/m3 (slate is a compact rock)
Water absorption: 0.1 - 0.6 % (low, slate has suffered by compaction an important dehydration, its porosity being a small one; however, slate needs waterproofing)
Hardness on the MOHS scale: 6-7 (slate is a pretty hard rock; diamond is considered the toughest and has a value of 10)
Porosity: low (due to significant compaction during formation)
Insulator: yes (electric)
Color: varied depending on the mineralogic composition (from black, when it contains organic material, to red, when it contains iron oxides); black, gray, green, mottled (the last is the most sought after and appreciated), rarely light colors.
Mineralogic composition: frequently composed of quartz and clay minerals (muscovite or illite) to which are added, in different proportions, other minerals (biotite, chlorite, hematite – they give green or reddish color to slate)
Organic composition: black slates contain organic animal and vegetable matter; sometimes fossils appear due to the low degree of metamorphism.
Uses
Various uses (ORNAMENTAL INTERNAL AND EXTERNAL MATERIAL BY THE MENTIONED PROPERTY).
First uses: roofs, writing boards for students, tombstones.
Modern uses: interior cladding (floors, ceilings, walls) and exterior; flexible slate (sheets of low thickness that can be applied to different curved shapes and which give an added elegance especially to furniture elements).
Origins
Rock is commonly found on the globe.
- The largest producer in Europe – Spain, UK, France
- Brazil is the second largest producer
- India (numerous varieties of color) and China – major Asian producers
- Romania – the slate warehouse in Deva
Flexible slate is a 1-2 mm thick veneer, laminated on a polymer composite substrate that will induce great flexibility and strength, making it suitable for curved shapes. The weight ranges from 2 kg/sqm to 2.2 kg/sqm.
SEDIMENTARY ROCKS
LIMESTONE/TRAVERTIN
Limestone is a sedimentary rock, dominant of organic origin, made up of calcite and aragonite (calcium carbonate minerals - CaCO3, but with different crystallization). In addition to the above-mentioned minerals, the limestones also have clay, quartz, gypsum, dolomite (calcium carbonate and magnesium).
As with marble, which comes from the metamorphosis of limestones, limestones have very varied colors in close connection with impurities in the rock (red and yellow from iron oxides, gray to black when they contain organic matter or manganese). White and gray colors are the most common.
As with most sedimentary rocks, most varieties of lime contain granules. In most cases, these granules are residues of the skeletons of marine organisms (predominant corals and foraminifers). The most widespread limestones on the globe are the reef limestones (reefs are constructions made by corals).
Some ironing does not contain granules at all, which are completely formed by chemical precipitation of calcite/aragonite. Such limestone rocks are formed by the precipitation of calcite due to the oversaturation of groundwater with calcium carbonate. Under certain conditions of temperature and pressure, oversaturated waters with dissolved calcite begin to precipitate by re-reading a variety of limestone which, depending on the origin, bears different names. Calcium carbonate precipitated in caves or at the origin of cold-water springs is called calcareous tun, and calcium carbonate with a fibrous appearance precipitated at the mouth of some hot springs is called travertine.
Chemical reactions that lead to the decomposition of limes require the presence in water of a weak carbonic acid, very corrosive to calcite. Calcium carbonate in contact with this carbonic acid turns into calcium bicarbonate which is highly soluble. This chemical reaction is responsible for the degradation of irons or travertines. As a building material, the most sought-after limestone is the one that contains a large amount of silica, this mineral being hard to soluble, and the durability of the limestone is greater. Travertine is specially treated so as not to be degraded by acid rain when used as an outdoor material.
GENESIS
Travertine is, therefore, a porous limestone formed by chemical precipitation and not by biotic processes (by marine organisms). The high porosity of travertine is due to the inclusion in the limestone mass of the organic vegetable debris which, over time, decomposes and in their place appear those gaps in the mass of the rock that characterize the travertine. In the modern processing of travertine, the gaps on the surface of the rock are filled with a special cement.
By grinding, the travertine acquires a glossy appearance that brings it closer in appearance to marble. The color varieties of travertine are more numerous than that of limestone. This aspect makes it a building rock much more sought after than limestone (travertine is one of the rocks with a very old use as a building material, easy to process and with special colors).
Properties
Limestone, travertine (natural state)
Hardness on Mohs scale 3 – 4 3 - 4
Density: 2.5 – 2.7 kg/cm3 2.71 kg/cm3
Water absorption: less than 1% high (due to gaps)
Porosity: very low (due to gaps)
High weather resistance (not water soluble)
weak (mechanical erosion)
Uses
Limestone has been used since ancient times as a building material, being also one of the most widespread sedimentary rocks on the globe (the pyramids of Egypt are built of limestone blocks, churches and castles from the Middle Ages, bank offices, railway stations from the 19th to the 20th centuries). The use of limestone is very varied, from the cement industry to agriculture (as a calcium solution to reduce soil acidity) and the pharmaceutical industry (toothpaste, medicines).
Travertine also has an ancient use. The oldest known career is in Italy (the quarry at Tivoli known during the Roman Empire, the rock here being used in aqueducts, viaducts, temples, Roman baths, amphitheaters as in the case of the Colosseum). The pleasant appearance of travertine (many varieties of colors alternating as strips) made it to be used especially as ornamental stone (pavements, facades of buildings, kitchen or bathroom countertops, cladding interior walls). It is easy to process, its modern presentation as a building material is that of tiles with varying thicknesses depending on the use.
Origins
Travertine occurs in many countries. Italy has a monopoly on the travertine market through high production and quality. Next up are Turkey, Iran, Mexico and Peru. In Romania we notice the travertine quarries of Geoagiu and Carpinis. From the rocks exploited from these quarries were made the Arc de Triomphe in Bucharest, as well as the famous sculptures of Brancusi ("The Table of Silence" and Poarta Sarutului "The Gate of the Kiss").
SANDSTONE
The sandstone is a rock in the category of sedimentary rocks formed by the cementing of sand. Depending on the nature of the cement, sandstone can be easily broken or very hard. Most sandstones are made up of quartz or feldspar because they are the most common minerals in the earth's crust. The color of the tiles is very varied, just as the sand has various colors: from black to white, yellow, pink, red, green, gray, gray, brown.
GENESIS
In the genesis of the mistakes, two distinct stages are noted:
a) the accumulation of sand resulting from the erosion of pre-existing rocks. Sand can accumulate in very different environments: rivers, lakes, marine or ocean basins, deserts.
b) after accumulation, the sand becomes sandstone when compacted by the pressure of the deposits that cover it and cemented it by precipitation of minerals that circulate as a solution through the spaces between the sand particles.
Cement is mostly made of calcium carbonate (calcareous mistakes) or silica (silicates, the toughest mistakes).
Properties
(valid for silica sandstone, the most resistant tiles)
Color: varied, usually light in color (yellow to white)
Density:2,3 – 2,4 kg/cm3
Hardness on the Mohs scale: 6.5 – 7 (very hard rock)
Porosity: very small
Water absorption: 1 – 1.2% (very low)
Weather resistance: very high.
Uses
By being relatively easy to process, sandstone has been used since ancient times (paleolithic) as a building material for houses or for various tools or sculptures (statues of deities). The tile is still used today as a building material with a wide range of uses: paving, walls, foundations, ornamental material or decorative stone (ghosts, arches, pavers, curbs), monuments, statues. Silica sandstone is used, by grinding, in the glass industry.
Origins
Sedimentary rock is commonly found on the globe (very used in India).
You can order all these types of rocks from piatraonline.ro, so that your projects are truly successful, elegant, but also very resistant over time.
Selective bibliography
Anastasiu N. (1987), Petrology of sedimentary rocks, Editura Tehnica, Bucharest
Mackenzie W.S., Donaldson C.H., Guilford C. (1988), Atlas of Igneous Rocks and Their Textures, Longman
Radulescu D. (1981), Magmatic and Metamorphic Petrology. Editura Didactica si Pedagogica, Bucharest
Seclaman M., Barzoi S.C., Luca A. (1999), Magmatic Petrology. Magmatic Systems and Processes, Editura Universitara, Bucharest.
