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Natural stone is a collective name for thousands of different types of stone, found and quarried throughout the world...

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about stone classification

What Determines A Stone's Characteristics?...

Origin - How was it made?

  • Sedimentary
  • Metamorphic
  • Igneous
  • Man-Made

Composition - What is it made of?

  • Silicates
  • Calcium Carbonates

 

Classification of Rocks

Rocks Classification

 

Mineral Composition

Silicates

These stones are made mostly of quartz-like particles called silica. They are very hard, durable and generally acid resistant. Examples: granite, sandstone, slate and quartzite.

Calcium Carbonates

The minerals in these stones were formed under pressure over millions of years from the bodies of tiny fossilized creatures. These stones are softer, less durable than silicates and acid sensitive.
Examples: limestone, marble and travertine.

 

Sedimentary Stone - "Cementing of Grains"...

Sedimentary stone came from organic elements such as glaciers, rivers, wind, oceans, and plants. Tiny sedimentary pieces broke off from these elements and accumulated to form rock beds. They were bonded through millions of years of heat and pressure.
Sedimentary rock is formed in three main ways:

-by the deposition of the weathered remains of other rocks (known as clastic sedimentary rocks);
-by the deposition of the results of biogenic activity; and
-by precipitation from solution.

Sedimentary rocks are formed from overburden pressure as particles of sediment are deposited out of air, ice, or water flows carrying the particles in suspension. As sediment deposition builds up, the overburden (or lithostatic) pressure squeezes the sediment into layered solids in a process known as lithification ("rock formation") and the original connate fluids are expelled.
Sedimentary rocks include common types such as chalk, limestone, sandstone, and shale.
These stones are formed through the compacting of grains or pieces of any kind of existing rock material. These existing rocks may have been weathered, transported, deposited and then cemented over millions of years by the movement of the earth's tectonic plates. From the formation of the continents to an earthquake or volcanic eruption, all of these events have helped form this stone.
Sedimentary stones may even contain fossils or other distinct features formed at the time of deposition.

Limestone: Mainly consists of calcite. It does not show much graining or crystalline structure. It has a smooth granular surface. Varies in hardness. Some dense limestones can be polished. Common colors are black, grey, white, yellow or brown. It is more likely to stain than marble. Limestone is known to contain lime from sea water.

Sandstone: Is a very durable formation of quartz grains (sand). Usually formed in light brown or red colors. Categorized by the most popular sandstone bonding agents such as silica, calcium, clay, and iron oxide.

Soapstone: A very soft stone made of a variety of talc. It is a dense mineral that wears well and is often resistant to stains.

Fossilstone: Considered a limestone that contains natural fossils such as sea shells and plants.

Travertine: Usually a cream or reddish color. It is formed through the accumulation of calcite from hot springs. It contains lots of holes that were formed from water flowing through the stone. These holes are often filled with synthetic resins or cements. Requires lots of maintenance if the holes are not filled. Classified as a limestone and a marble.

Sedimentary rocks are composed largely of silica (i.e. quartz), with other common minerals including feldspars, amphiboles, clay minerals and sometimes more exotic igneous minerals. Sedimentary rocks are classified as clastic, that is, they are composed of discrete clasts of material (rather than being composed of organic material as is the case for a limestone).
Carbonate minerals precipitating out of the ocean cover the ocean floor with layers of calcite which can later form limestone. Sedimentary rocks are economically important in that they can be used as construction material. In addition, sedimentary rocks often form porous and permeable reservoirs in sedimentary basins in which petroleum and other hydrocarbons can be found.
It is believed that the relatively low levels of carbon dioxide in the Earth's atmosphere, in comparison to that of Venus, is due to large amounts of carbon being trapped in limestone and dolomite sedimentary layers. The flux of carbon from eroded sediments to marine deposits is known as the carbon-cycle.
The shape of the particles in sedimentary rocks has an important effect on the ability of micro-organisms to colonize them. This interaction is studied in the science of geomicrobiology. One measure of the shape of these particles is the roundness factor, also known as the Krumbein number after the geologist W. C. Krumbein.

 

Metamorphic Stone - "Changed in Structure"

Metamorphic stone originates from a natural change from one type of stone to another type through the mixture of heat, pressure, and minerals. The change may be a development of a crystalline formation, a texture change, or a color change.

Metamorphic rocks result from mineralogical and structural adjustments of solid rocks to physical and chemical conditions differing from those under which the rocks originally formed. Changes produced by surface conditions such as compaction are usually excluded. The most important agents of metamorphism are temperature, and pressure. Equally as significant are changes in chemical environment that result in chemical recrystallization where a mineral assemblage becomes out of equilibrium due to temperature and pressure changes and a new mineral assemblage forms.

Three types of metamorphism may occur depending on the relative effect of mechanical and chemical changes.

-Dynamic metamorphism, or cataclasis, results mainly from mechanical deformation with little long-term temperature change. Textures produced by such adjustments range from breccias composed of angular, shattered rock fragments to very fine-grained, granulated or powdered rocks with obvious foliation and lineation termed mylonites.
-Contact metamorphism occurs primarily as a consequence of increases in temperature where differential stress is minor. A common phenomenon is the effect produced adjacent to igneous intrusions where several metamorphic zones represented by changing mineral assemblages reflect the temperature gradient from the high-temperature intrusion to the low-temperature host rocks; these zones are concentric to the intrusion. Because the volume affected is small, the pressure is near constant. Resulting rocks have equidimensional grains because of a lack of stress and are usually fine-grained due to the short duration of metamorphism.
-Regional metamorphism results from the general increase of temperature and pressure over a large area. Grades or intensities of metamorphism are represented by different mineral assemblages. Regional metamorphism can be subdivided into different pressure-temperature conditions based on observed sequences of mineral assemblages. It may include an extreme condition, where partial melting occurs, called anatexis.

Other types of metamorphism can occur. They are retrograde metamorphism, the response of mineral assemblages to decreasing temperature and pressure; metasomatism, the metamorphism that includes the addition or subtraction of components from the original assemblage; poly-metamorphism, the effect of more than one metamorphic event; and hydrothermal metamorphism, the changes that occur in the presence of water at high temperature and pressure which affect the resulting mineralogy and rate of reaction.

-Hydrothermal metamorphism
Hydrothermal metamorphism is the result of the interaction of a rock with a high-temperature fluid of distinct composition. The difference in composition between protolith and fluid triggers a set of methamorphic reactions. This kind of metamorphism is responsible for many economic metal deposits. Convection circulation of water in the ocean floor basalts produces extensive hydrothermal metamorphism.

-Impact metamorphism
This kind of metamorphism occurs when an extraterrestrial object (a meteorite for instance) collides with the Earth's surface, or, during an extremely violent volcanic eruption. Impact metamorphism is, therefore, characterized by ultrahigh pressures conditions and low temperature. The resulting minerals (such as SiO2 polymorphs coesite and stishovite) and textures are characteristic of these conditions.

Marble and slate are metamorphic stones. They were formed at extremely high pressures and temperatures below melting. The presence of swirls, linear patterns or banding is a key characteristic. Slate is a fine grained, metamorphic rock, which cleaves in flat, almost smooth pieces. Marble is a metamorphic limestone that loses the fossils and other features during the recrystallization.

Marble: A recrystallized limestone that formed when the limestone softened from heat and pressure and recrystallized into marble where mineral changes occurred. The main consistency is calcium and dolomite. Ranges in many colors and is usually heavily veined and shows lots of grains. Hardness rates from 2.5 to 5 on the MOH Scale. Marble is classified into three categories(Stone World):

1. Dolomite: If it has more than 40% magnesium carbonate.
2. Magnesian: If it has between 5% and 40% magnesium carbonate.
3. Calcite: If it has less than 5% magnesium carbonate.

Slate: A fine grained metamorphic stone that formed from clay, sedimentary rock shale, and sometimes quartz. Very thin and can break easily. Usually black, grey, or green.

Serpentine: Identified by its marks which look like the skin of a serpent. Most popular colors are green and brown. Hardness rates from 2.5 to 4 on the MOH Scale. Contains serpentine minerals has lots of magnesium, and has an igneous origin. Does not always react well to recrystallization or diamond polishing.

 

Igneous Stone - "Born of Fire"

Igneous stones are mainly formed through volcanic material such as magma. Underneath the Earths surface, liquid magma cooled and solidified. Mineral gases and liquids penetrated into the stone and created new crystalline formations with various colors.

Igneous rocks are formed from the solidification of magma, which is a hot (600 deg.C - 1300 deg.C, or 1100 deg. - 2400 deg. F) molten or partially molten rock material. The Earth is composed predominantly of a large mass of igneous rock with a very thin covering of sedimentary rock. Whereas sedimentary rocks are produced by processes operating mainly at the Earth's surface such as weathering and erosion, igneous--and metamorphic--rocks are formed by internal processes that cannot be directly observed.

Igneous rocks are formed when molten rock (magma derived from the mantle, or, pre-existing rocks molten by extreme temperature) cools and solidifies, with or without crystallization. Over 700 types of igneous rocks have been described, most of them intrusive.

Igneous rock are geologically important because:

-Their minerals and global chemistry gives information about the composition of the mantle where they were extracted from, and the temperature and pressure conditions that allowed this extraction, or (below) their minerals and global chemistry gives information about the composition of the country pre-existing rock that melted
-Their absolute ages can be obtained from various forms of radiometric dating and thus can be compared to adjacent strata, allowing a time sequence of events.
-Their features are usually characteristic of a specific tectonic environment, allowing tectonic reconstitutions.
-In some special circumstances they host important mineral deposits, of, for example, tungsten, tin or uranium, commonly associated with granites they can be explored as ornamental stone.

Igneous rocks are classified according to mode of occurrence, texture, chemical composition, and the geometry of the igneous body.

Granite comes from igneous rocks, formed slowly, as it cooled deep underground. Their minerals look like small flecks typically spread consistently throughout stone. Some other types have veining (linear waves) like marble. They are hard (cannot be scratched by steel) and dense.

Granite: Primarily made of Quartz (35%), Feldspar (45%) and Potassium. Usually has darker colors. Contains very little calcite, if any. Provides a heavy crystalline and granular appearance with mineral grains. It is very hard material and easier to maintain than marble. Yet, it is still porous and will stain. There are different types of granite depending on the percentage mix of quartz, mica and feldspar. Black granite is known as an Anorthosite. It contains very little quartz and feldspar and has a different composition than true granite.

Man Made Stones are derived of unnatural mixtures such resin or cement with the additive of stone chips.

Terrazzo:

Marble and granite chips embedded in a cement composition.

Agglomerate or Conglomerate:

Marble chips embedded in a colored resin composition.

Cultured or Faux Marble:

A mix of resins that are painted or mixed with a paint to look like marble.

Quartz (Composite):

Quartz (Composite) is made using a combination of 93 % Quartz, Quartz Silica, Granite or Recycled Mirror*, combined with 7 % resin, colors and binders. This mixture is pressed into 52" X 120" sheets using a unique and proprietary vibration-vacuum-compression process. The sheets are then heat treated, cooled, ground (calibrated) and polished to a high gloss shine.