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The Gemstone Granite


I have always known that granite was a very versatile material. But only recently while looking around on the internet, did I find out, just how versatile granite really is. We are primarily interested in it's uses as a gem or decorative material. But I now see it has many uses.

Pink Granite Sphere
One decorative granite item we have seen a lot of, is the granite sphere. Granite spheres come in many great colors. There is a very nice granite from Llano, Texas called Llanoite. Llanoite is a very fine-grained granite with floating feldspar and blue quartz in it. The blue quartz gets it's coloration from ilmenite inclusions. Llanoite makes very nice gemstones along with being a nice decorative stone. To the right is a pink granite sphere We have seen
many of granite's other colors used as gemstones too.

Granite Composition:
Granite is an igneous rock that is composed primarily of four minerals. Magma cooling very
slowly far under the earth's surface, allows crystals of the four minerals to grow large enough to be easily seen by the naked eye. These minerals are quartz, feldspar, mica, and usually hornblende. However granite is not a homogenous rock and it's composition varies depending on its location. Other less common components give granite a wide variation in look and color.

The geological definition of granite is "any plutonic rock in which the mineral quartz makes up 10 to 50 per cent of the felsic components, and the ratio of alkali to total feldspar is between 65 and 95 per cent." However you may find that commercial suppliers may not be so specific. They may use the name granite on any of the other holocrystalline quartz-bearing plutonic rock and of course these types of rock do look like granite and may have many of it's properties.

Some Granite Properties:
Feldspar with a hardness of 6 and quartz with a hardness of 7, give granite its exceptional abrasion resistance. Which makes granite so useful as a commercial building material.

Some granites change relatively little with changes in temperature. Which also makes granite a good choice for high precision applications that require little change due to temperature.

Flexural strength, or the ability to resist bending force. Makes granite a good material for load bearing applications

Granite is also resistant to many acids and other caustic chemicals. So it is often used as a liner in commercial vats and such. This also makes granite good for applications that are below grade in contact with soil and water.

Some Facts and History:

Granite is the state stone for North Carolina

The term granite comes from the Latin root word granum, meaning "grain".

The state of New Hampshire has the nickname "Granite State"

Granite is quarried and used for many things on a world wide scale.

The Four Main Minerals:

quartz is a common mineral that is found in many different types of rocks. The chemical formula is Silicon oxide (SiO2). Impurities in the rock at the time of formation causes the quartz crystal to produce different colors. Quartz can be colored yellow, milky white, rose, brown to black, blue and the best known color purple amethyst.

Feldspar is the most abundant mineral in rocks that are located at or near the earth's surface. Feldspar can have a glassy white, blue, green, pink or red crystals. When feldspars are exposed to the atmosphere they weather easily. Clays are formed by weathered feldspar.
Kaolinite is the highest quality of the feldspar clays used by potters.

Hornblende is a mineral that contains magnesium, iron, silica and aluminum. Hornblende is black, brown and green in color. It occurs in crystals of many igneous rocks.

Mica can be clear, black, green, red, yellow, brown, purple lapidolite and other colors too. Clear mica was named Muscovite because it was found near Moscow, Russia. It was used as window glass in the Muscovite's homes. Muscovite contains water which helps to make it clear. Biotite mica is dark green to black in color because it contains metals such as iron and magnesium.

As you can see the different colors produced by these four minerals alone can give granite many different colors. Add other accessory minerals and loosely associated types of granite and you get quite an array of colors. Below is a link to a page that has dozens of different granite colors. If you are interested.

If you want to learn all there is to know about granite. Click on the link below. This is a site devoted to granite links.

Granite HQ
All types of granite information