igneous
Granite Pebble
Granite (a phaneritic intrusive igneous rock consisting of quartz, alkali feldspar, and plagioclase)
Hardness: 6-7 on Mohs scale; Color: typically mottled pink, gray, or white; Luster: dull to vitreous; Crystal Structure: phaneritic (coarse-grained) with interlocking crystals; Cleavage: none (fractures irregularly); Specific Gravity: 2.63 to 2.75
- Hardness
- 6-7 on Mohs scale
- Color
- typically mottled pink, gray, or white
- Luster
- dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: typically mottled pink, gray, or white; Luster: dull to vitreous; Crystal Structure: phaneritic (coarse-grained) with interlocking crystals; Cleavage: none (fractures irregularly); Specific Gravity: 2.63 to 2.75
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground. This specific specimen has been further shaped by fluvial or glacial erosion into a rounded cobblestone or pebble form. Its geological age can span from the Archean Eon to the Cenozoic Era depending on the specific pluton of origin.
Uses & applications
In pebble form, it is used for landscaping, garden pathways, and drainage. In larger quarried blocks, granite is ubiquitous in construction (countertops, monuments, paving) due to its durability and resistance to weathering.
Geological facts
Granite makes up the majority of the Earth's continental crust. Because it contains significant amounts of potassium-40, granite can be slightly radioactive compared to other rock types. The term reflects the Latin 'granum' (grain) referring to its coarse crystalline texture.
Field identification & locations
Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals of different colors. It is most commonly found in continental mountain ranges and riverbeds downstream from batholiths. Collectors should look for its inability to be scratched by a steel knife and the lack of reaction to acid.
