Geological origin of Stone
The stones are rocks that present themselves in a solid state being formed by one or more minerals which is part of the Earth crust and may be sharply individualised. The minerals formed from the rocks are composed by silicon, aliminium, iron, calcium, sodium, potassium and magnesium combined with oxygen and normally they are under the crystalline form.
About the genesis, the rocks are classified into three major groups:
- Magmatic rocks or igneous
- Sedimentary rocks
- Metamorphic rocks
Magmatic Rocks or Igneous
Resulting from the solidification of magma, their texture depends on the size and arrangement of the constituent minerals.
The rocks that result from the consolidation at depth are called Platonic or magnetic intrusive rocks, for example granite, the other are volcanic or extrusive igneous rocks, for example basalt.
Sedimentary rocks
These rocks are formed by the deposition of debris originating from the breakdown of pre-existing rocks or by the accumulation of organic animal or plant materials or by chemical precipitation of dissolved salts in the waters of rivers, lakes and seas.
Sedimentary rocks can also be classified as:
Detrital Sedimentary Rocks:
From the disaggregation of pre-existing rocks (sandstone)
Chemical Sedimentary Rocks:
Resulting from the precipitation of substances wich are dissolved (Limestone)
Organic Sedimentary Rocks:
Formed by the accumulation of animal and plant debris (Peat)
Residuals Sedimentary Rocks:
It results from soil hardened by precipitation of iron and aluminium hidroxides or other compounds.
Metamorphic Rocks
Metamorphic rocks (shape shifters; meta=change, morphos= way) result, as noted above, the processing of any type of rock, when it is subjetecd to an environment where the physical conditions (pressure and temperature) are very different from those whiche the same was formed.
Examples of Metamorphic Rocks
- Sandstone -> Quartzite
- Pure Limestone -> White Marble
- Dolomitic Limestone-> Green Marble
- Granite -> Gneiss
- Basalt -> Shale Green