NATURAL STONE HISTORY & TYPES
The familiar stone types that are used today are identified through four categories:
Sedimentary, Metamorphic, Igneous and Man-made stone.
I. Sedimentary stone came from organic elements such as glaciers, rivers, wind, oceans, and plants. Tiny sedimentary pieces broke off form these elements and accumulated to form rock beds. They were bonded through millions of years of heat and pressure.
a)Limestone: Mainly consists of calcite. It does not show such graining or crystalline structure. It has a smooth granular surface. Varies in hardness. Some dense limestone 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.
b)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.
c)Soapstone: A very soft stone made of a variety of talc. It is a dense mineral that wears well and is often resistant to oxide.
d)Fossil stone: Considered a limestone that contains natural fossils such as sea-shells and plants.
e)Travertine: Usually a cream or reddish color. It is formed through the accumulation of calcite from hot springs. It contains holes that were formed from water flowing through the stone. These holes are often filled with synthetic resins or cements. Requires a lot of maintenance if the holes are not filled. Classified as a limestone and a marble.
II. Metamorphic stones originate from a natural form of 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.
a)Marble: A recrystallized limestone that formed when the limestone softened from heat and pressure and recrystallized into marble where a mineral change occurred. The main consistency is calcium and dolomite. Ranges in many colors and is usually heavily veined and shows grains. Hardness rates from 2.5 to 5 on the MOH Scale.
Marble is classified into three categories:
1. Dolomite: If it has more than 40% magnesium carbonates.
2. Magnesium: If it has between 5% and 40% magnesium
3. Calcite: If it has less than 5% magnesium carbonate.
b)Slate: Fine grained metamorphic stone that is formed from clay, sedimentary rock shale, and sometimes quartz. Very thin and can break easily. Usually in black, gray or green.
c)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 and magnesium, and has an igneous origin. Does not always react well to recrystallization or diamond polishing.
III. Igneous stones 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.
a)Granite: Primarily made of Quartz (35%), Feldspar (45%) and Potassium. Usually comes in dark colors and contains very little calcite, if any. Provides a heavy crystalline and granular appearance with mineral grains. It is a 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.
IV. Man Made Stones are derived of unnatural mixtures such as resin or cement with the additive of stone chips.
a)Terrazzo: Marble and granite chips embedded in a cement composition.
b)Agglomerate or conglomerate: Marble chips embedded in a colored resin composition.
c)Cultured or Faux Marble: A mix of resins that are painted or mixed with a paint to looks like marble.