igneous
Granite with Orthoclase and Hematite Staining
Phaneritic Felsic Igneous Rock (primarily SiO2 with KAlSi3O8)
Hardness: 6-7 on Mohs scale; Color: Mottled tan, grey, and pink/rust; Luster: Dull to vitreous; Crystal structure: Phaneritic (coarse-grained); Cleavage: Good in two directions for feldspar components; Specific gravity: 2.6-2.7 g/cm³
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled tan, grey, and pink/rust
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Mottled tan, grey, and pink/rust; Luster: Dull to vitreous; Crystal structure: Phaneritic (coarse-grained); Cleavage: Good in two directions for feldspar components; Specific gravity: 2.6-2.7 g/cm³
Formation & geological history
Formed through the slow crystallization of magma below Earth's surface. The pinkish-red staining is likely caused by secondary iron oxide (hematite) or a high concentration of potassium-rich orthoclase feldspar. Age can range from Precambrian to Cenozoic depending on the specific pluton.
Uses & applications
Used extensively in construction as aggregate, countertops, and decorative masonry. Smaller rough specimens like this are primarily used for geological study or classroom examples.
Geological facts
Granite makes up the majority of the Earth's continental crust. The distinct red/purple patch on this specimen suggests localized oxidation or hydrothermal alteration after the initial rock solidified.
Field identification & locations
Identify in the field by looking for visible interlocking crystals of quartz and feldspar; look for its high resistance to weathering. Found globally in mountainous regions. Collectors should look for unique mineral inclusions or large phenocrysts.
