Types of Stone & Other Facts

TYPES OF STONE:

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)Fossilstone: 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.


STONE NAMES

Currently, there are many companies around the world that use generic names to identify different types of stone. This has created a problem for the stone maintenance industry. The original names were in Italian. Usually the name consists of two parts. The first part describes the color and second part describes the name from where the stone was quarried.

 

ITALIAN NAME ENGLISH COLOR
Azzuro Blue
Breccia Broken Pieces
Dorato / D'oro Gold
Fiore Flower
Giallo Yellow
Negro/ Nero Black
Perla/ Perlato Pearl
Rosa Pink
Rosso Red
Verde Green
Bianco White


Example:
Negro Marquina is a black limestone from Marquina, Spain.
Bianco Carrara is a white marble from Carrara, Italy.

 



TYPES OF SURFACE TEXTURES

There are many different types of stone available today. When stone is ordered, it is fabricated with a particular type of surface. There are six main type of surfaces that are selected:

Honed: Provides a flat to low sheen gloss. Different levels of gloss can be selected. This surface is very smooth, but often very porous. This texture is common in high traffic buildings. Honed floors should always be protected with Penetrating Sealer because it has wide-open pores. Honed stone colors are not as vibrant as polished stone.

Polished: A glossy surfaces that wears away with time due to heavy foot traffic and using improper maintenance procedure. This surface is very smooth and not porous. The reflectively of polished crystals brings out the brilliant colors and grains of natural stone. The shine comes from the natural reflection of the stone's crystals. The shine is due to polishing bricks and polishing powders used during fabrication. The Shine is not from a coating.

Flamed: A rough surface that is developed through heat. During fabrication, the stone is heated up and the crystals begin to pop, thus forming a rough surface. This surface is very porous and must be treated with an impregnator.

Sand Blasted: This surface is the result of a pressurized flow of sand water that provides a textured surface with a matte gloss.

Sawn: A Process performed by using a gang saw.

Bush Hammered: A pounding action that develops a textured surface. The degree of roughness can be selected.

Regardless of the type of surface to be maintained, all stone should be protected with sealers.


COLORS 

As discussed previously, stone was formed from different types of natural minerals. Marble's main consistency is calcium. Calcium carbonate is the natural source that bonds the stone. Certain additive minerals blended into during formation to customize these brilliant colors. The additive minerals are also color developers present in granite and other natural stones.

 

Stone Color Mineral
Black Biotite, Hornblende, Carbon
Brown Limonite
Gray Variety of minerals
Green Mica, Chloride, Silicate
Red Hematite
White Feldspar, Calcite, Dolomite
Yellow Limonite

 

Mineral Mineral Color
Augite Brown, Green, Black, Purple
Biotite Black, Brown, Green
Calcite Pearlenscent and Pale Colors
Dolomite Colorless, Pink, Pale Brown
Feldspar Yellow, White, Pink, Green, Grey
Hematite Metallic Grey or Black
Hornblende Green, Yellow, Brown, Black
Limonite Black, Brown, or Yellow
Sulphur Pale Gold

      
Minerals have a variety of crystalline properties. For instance, Augite (listed above) has different crystalline properties. Each property has its own color. Stones brilliant colors and various crystal formations developed when different mineral properties blended together along with the integration of temperature and pressure.

The veins and color grains of marble were liquid minerals that flowed through the stone when the Earth heated up. The intense heat softened the limestone to allow the liquid to flow through it. When the Earth cooled, the mineral flow stopped and gradually hardened to its state.

The delicate colors of stone often can altered by the improper use of cleaning chemical, mopping with dirty be solution, using chemicals that are not designed for stone care, and sunlight can fade the color of natural minerals.

 



REFLECTIVITY OF STONE 

Stone contains natural crystals. These crystals reflect light to provide a shine on the surface. When the crystal, dull, crushed, or broken, they cannot reflect light evenly. For Example, when the lens of a flashlight breaks, it cannot reflect the light that is being emitted form the bulb.

Polished stone floors become dull when heavy foot traffic along with sediment erodes the crystals. Normal footwear does not cause the main damage, sediment and grit do. The sediment and grit that lies on the stone surface is the main enemy of stones crystal. The damage to the crystals occurs when the pressure from the shoe forces the sediment to abrade or fracture the crystals.

The only safe way to restore and sharpen the crystal is to polish them with diamond abrasives or polishing powders. The life span of crystal can be extended by administering a thorough dust mopping program with a proper moping and maintenance system. Extensive entrance matting is extremely important because it keeps exterior sediment from entering a building.

 



THE HARDNESS OF STONE

Marble is a relatively soft stone. On a measurement of hardness of (MOHS), marble is approximately a three out of ten. Marble is made of calcium, just like your teeth. If you eat something too hard you will break your tooth. If you eat a lot of sugar you will get a cavity. Stone reacts the same way. If an improper chemical is applied to the surface, corrosion will begin to form cavities in the stone. 

 

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