Stones are classified base on 2
criteria : how they are made, and what composes them.
Stones were formed a long time ago according
to 3 different processes
1 - Born of fire : the Igneous Stones.
These are stones that were once very
hot and liquid and cooled down underground. Their grains look like
small flecks typically spread consistently throughout stone. They are
hard (cannot be scratched by steel) and dense.
Granite is a typical igneous stone used
in mosaic.
 |
| Blue Granite |
2 - Sedimentary Stones
These stones are formed through the
compacting of grains or pieces of any kind of existing rock material.
These existing rocks may have been weathered, transported, deposited
and then cemented over millions of years by the movement of the
earth’s tectonic plates. Sedimentary stones sometimes contain fossils or other
distinct features formed at the time of deposition.
Limestones and Travertines are
sedimentary stones used in mosaic.
 |
| Raw travertine |
 |
| Gold Travertine |
3 - Metamorphic Stone –
“Changed in Structure”
They were formed at extremely high
pressures and temperatures but did not melt like igneous stones did.
The presence of swirls, linear patterns or banding is a key
characteristic of metamorphic stones
Marble, Agates, and Slate are
metamorphic stones used in mosaic.
 | |
| Raw agate |
 | |
| 4 slates. |
 | |
| Marble. |
2 . Mineral Composition of Stones
Stones basically made of 2 different stuffs : Silicate (Silicium Oxyde SiO2) and Calcium Carbonate (CaCO3)
21 - Silicates
These stones are made mostly of
quartz-like particles called silica. They are very hard, durable and
generally acid resistant.
Granites, Flint and Slates are Silicates used in mosaic.
22 - Calcium Carbonates
The minerals in these stones were
formed under pressure over millions of years from the bodies of tiny
fossilized creatures. These stones are softer, less durable than
silicates and acid sensitive.
Limestones, Marbles and Travertines are
Calcium Carbonates used in mosaic.
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| Tesshu's Tiger - Travertine and Granite |
