Types of Stones
Natural stones are classified according to their mineral content and the process of their formation. Most of these minerals can be identified by their color, hardness and crystal formation. However, wide arrays of minerals are often difficult to identify. Many stones look similar to each other, but are actually different. Good stones are characterized by durability, hardness, strength, amenability to dressing, appearance, and weight, fineness of grain, compactness, porosity and absorption.
In order to be suitable as building stones, a rock should have specific qualities such as capacity to stand the ravages of time and weather, requisite strength to bear strain and super-incumbent weight, attractive color and general appearance. Its structure must also be such as to allow quarrying into good sized blocks or planes. India possesses extensive deposits of different kinds of building and monumental stones. It is one of the few major countries known for the production and export of natural building stones of various coolers. The most important building stones in India are the granites, allied rocks, sandstone, limestone, slate and marble. The different types of stones are:
I. Sedimentary Stones
These stones came from organic elements such as glaciers, rivers, 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. Major types of sedimentary stones are:
Limestone
Mainly consisting of calcite, it does not show much graining or crystalline structure. It has a smooth granular surface and varies in hardness. Some dense limestone can be polished and is more likely to stain than marble. Common colors are black, grey, white, yellow or brown. Limestone is known to contain lime from sea water, and that's why the nomenclature.
Sandstone
Sandstone is a sedimentary stone that is typically the result of quartzite stone being eroded and redeposit by either wind or water. Sandstone mostly consists of quartz, silica, iron oxide and calcium carbonate and are durable, weather, acid and thermal resistant and have crushing strength. Sandstones are most highly craft able and manageable, they can at most take a honed polish, and are used as garden and commercial landscapes, exterior wall claddings, panels, pillars, sculptures, arches, etc. They come in an array of colors & shades and can be chiseled and dressed to a smooth surface in various attractive shapes.
Soapstone
It is a very soft stone made of a variety of talc. It is a dense mineral that wears well and is often resistant to oxide.
Travertine
Usually it has a cream or reddish color and 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 and require lots of maintenance if the holes are not filled.
II. Metamorphic Stones
These stones originates as a result of natural change from one type of stone to another type by the mixed action of heat, pressure and minerals. The change may be a development of a crystalline formation, a texture change, or a color change.
Marble
The term "Marble" is derived from the Latin word "Marbles" which itself comes from the Greek root "Marabous" meaning thereby a shining stone. Marble is a metamorphic rock resulting from the re-crystallization of limestone softened from heat and pressure. Main constituents are calcium and dolomite. Hardness ranges from 2.5 to 5 on the MOH scale. Marble is usually heavily veined and shows lots of grains. Dimensional marble specifications include smooth textures, ease in crafting sculptures, hence highly manageable. It is a reasonably strong and durable stone. It takes good polish, popularly used as wall claddings, floors, skirting’s table tops, treads and risers, sculptures, artifacts, etc. Marble is classified into three categories:
- Dolomite: If it has more than 40% magnesium carbonates.
- Magnesium: If it has between 5% and 40% magnesium.
- Calcite: If it has less than 5% magnesium carbonates.
Slate
Slate is a very fine grained metamorphic rock derived from the sedimentary rock 'shale'. Slate is composed mostly of mica, chlorite and quartz. Characteristically, the rock may slit into relatively thinner slabs and can break easily. Some slates take very good polish, are extremely beautiful and more cost effective than most other wall and floor coverings. Slate has a fine to medium grained surface texture. It renders a very graceful, natural finish to any building or home.
Serpentine
It is identified by its marks, which look like the skin of a serpent. Hardness rates from 2.5 to 4 on the MOH scale and most popular colors are green and brown. Contains lots of magnesium, and has an igneous origin. It does not always react well to recrystallization or diamond polishing.
III. Igneous Stones
These rocks are mainly formed through volcanic material such as magma. Underneath the earth's surface, liquid magma cooled and solidified. Mineral gases and liquids penetrated into the stone and created new crystalline formations with various colors.
Granite
The term "Granite" is derived from the Latin word "Granite" meaning "grain" because of its granular nature. Granite is an Igneous Stone, primarily made of Quartz (35%), Feldspar (45%) & Potassium. Dimensional granite specifications include high load bearing capacity, amenability to cutting without secondary flaws, ability to yield thin and large slabs and - above all - durability. Granite is a very strong and durable stone. It takes heavy gloss polish, popularly used as architectural stone for interior and exterior walls, floors and monumental stone.
IV. Man Made Stones
These stones are derived from unnatural mixtures such resin or cement with the additive of stone chips.
Terrazzo
Marble and granite chips embedded in a cement composition.
Agglomerates or Conglomerates
Marble chips embedded in a colored resin composition.
Cultured or Faux Marble
It is a mix of resins that are painted or mixed with a paint to look like marble.