Types of Stone

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Stone is a natural solid formation of one or many minerals. There are thousands of types of stone that have been quarried through the centuries. Quarries are located all around the world. A majority of natural stone comes from Italy, Spain, Turkey, United States, Mexico, China, Taiwan, India, Greece, Canada, France, and Brazil.



The minerals in stone came from the same liquid and gas minerals that formed the earth. The Earth developed as a massive body of gas and liquid minerals that slowly cooled and condensed to a solid core. Through pressure, the Earth s crust began to form and heavy minerals were forced down to the core of the Earth where they were trapped. As the crust got thicker, it squeezed around the inner core which created intense pressure and heat from within the Earth. Crystals and other solid forms began to grow from the mineral vapors that were being released. As the Earth s crust began to expand and erode, heat and pressure pushed the solid minerals up to the Earth s surface which formed colossal rock beds. It took up to one-hundred million years to form some of these beds. Many of the beds are now used as quarries where the stone is mined.



Most of these minerals can be identified by their color, hardness, and crystal formation. Crystals come in a variety of shapes and sizes. The wide array of these minerals are often difficult to identify. Many stones look very similar to each other. however, they are all very different.



TYPES OF STONE



The familiar stone types that are used today are identified through four categories: sedimentary, metamorphic, igneous stone, and man-made.



I. 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.



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.



II. Metamorphic Rocks: 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.



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:



1. Dolomite: If it has more than 40 magnesium carbonate.



2. Magnesium: 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.



III. 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.



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.



IV. 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.