Commercial Granites at KitchenAndGranite.com

• Granite Description
• True Granites vs. Commercial Granites
• True granite and true marble
• Metamorphic Rocks
• Water Absorption
• Similar Stones
• Basis of Name

True granite and true marble

Comparison of true granite and true marble. Schematic images are magnified.

In commercial granites, the larger the grain size, the lower is the strength, and the greater is the brittleness, because mineral cleavage can occur more easily in larger grains. A homogenous structure or a mildly-oriented one is a feature of magmatic rocks & so they have a similar appearance (structure) even over a large area of a slab. Metamorphic rocks are characterised by structures with bands, schlierens, & waves & so every part of a slab usually has a different appearance.

Every commercial granite contains feldspar of 6 Mohs Hardness of various colours white, pink, red, yellow, brown, green and grey. Feldspar grains are typically not translucent and are with cleavage. Many granites, especially of lighter colours, contain quartz of 7 Mohs Hardness with grey (sometimes bluish, brownish) colour and the grains are glassy translucent without cleavage. Further, there are dark minerals such as hornblende, pyroxene and biotite with black, dark green or dark brown colours. These minerals have larger specific gravity and lower hardness than feldspars and quartz. Some granites (e.g. KASHMIR WHITE) contain garnet of almost round shape and brown to dark-red colour.

The more the quartz, the lighter is the granite in colour, the larger is the microcrack porosity (because quartz volume decreases during crystalization), and so the lower is the strength, and the lower is the resistance to fire. The darker the granite, the more are the dark minerals, and the heavier is the granite.

Granites are hard and not scratchable by a nail, knife or glass piece unlike marbles. Depending on the feldspars and quartz portions, the total Mohs Hardness of granite is from 5.5 to 7. The darker the granite, the lesser is the quartz, and thus the lower is the hardness.
Commercial granites are not affected by common organic acids such as a lemon acid and vinegar, contrary to marbles.
How to use the table below?
Explanation of every column in the table is given below.

COMMERCIAL NAME & COUNTRY, STATE, PROVINCE

In the first column, the most frequently used or the most suitable names are presented alphabetically. The geographical location can help you source or select a stone.

COLOURS

In this column typical colours are stated according to their importance. While some variations are possible, this column can help you select or shortlist stones

PETROGRAPHIC TYPE

As mentioned, commercial granites have different origins and compositions: & this is an important consideration for the application for which the stone is used.

MAGMATIC ROCKS were formed by crystalization from magma. Many commercial granites are magmatic (igneous) rocks created some kilometers under the earth's surface. These so-called plutonic rocks are composed of visible mineral grains of equal size or some grains larger than others - porphyritic structure (e.g. SAPPHIRE BROWN). The grains are typically without orientation (e.g. RUBY RED), but there are also oriented plutonic rocks (e.g. SALISBURY PINK). Classification is based on mineral content as follows.

Granite group - rich in quartz (20 - 60 %) and feldspars (K-feldspars, Na-Ca-feldspars - plagioclases).
Granite feldspars (K-feldspars more than plagioclases), quartz, a little mica
- light grey, pink, red, white, yellow, brown colour.
Granodiorite - feldspars (plagioclase more than K-feldspar), quartz, a little dark mica, biotite. It is mainly of grey colour.
Pegmatite - very coarse rock of granite composition created in dykes.
Syenite group - rich in K-feldspars with less plagioclase and quartz (up to 20 %).
Syenite - feldspars (K-feldspars more than plagioclases), less biotite, hornblende.
Quartz syenite - feldspars (K-feldspars more than plagioclases), less quartz, biotite, hornblende.
Larvikite - special feldspars, small quantity of quartz, pyroxene, magnetite.
Monzonite - feldspars (K-feldspars = plagioclases), less biotite, hornblende, pyroxene.
Quartz monzonite - feldspars (K-feldspars = plagioclases), less quartz, biotite, hornblende, pyroxene.
Diorite group - rich in plagioclase, biotite, hornblende and pyroxene. It is usually of dark-grey colour.
Diorite - plagioclase, biotite, hornblende and pyroxene, small amount of K-feldspar and quartz.
Gabbro group - rich in plagioclase, pyroxene and olivine. It is usually of dark-grey to black colours.
Gabbro - plagioclase, pyroxene and less olivine.
Anorthosite - plagioclase, small quantity of pyroxene and olivine.
Dolerite - fine-grained rock of gabbro composition formed in dykes. Older name - diabase. It is transition between gabbro and basalt.

Charnockite group is rich in feldspars (K-feldspars, plagioclases) with less quartz and pyroxene.
This special group can be mainly added to granite group or to syenite group according to their composition.


Table showing the composition of magmatic rocks used as commercial granites.

Minerals	Plagioclase 10-35%	Plagioclase 35-65%	Plagioclase 65-90%	Plagioclase 90-100%
Quartz 20-60%	Plagioclase 35-65%		Granodiorite
Quartz 5-20%	Quartz syenite	Quartz monzonite
Quartz 0-5%	Syenite	Monzonite		Diorite Anorthosite Gabbro

Notes:

1. Plagioclase calculated from total feldspar content
2. Quartz calculated from total light minerals (quartz and feldspars)
3. yellow = granite group
4. green = syenite group
5. blue = diorite and gabbro groups
6. charnockites belong to granite or syenite groups
7. blank areas are rocks which are almost neverused as natural stones for construction