1. Mineral Composition:
* Granite: Predominantly quartz (SiO2) and alkali feldspar (orthoclase and albite), with lesser amounts of plagioclase feldspar, mica (biotite or muscovite), and hornblende.
* Gabbro: Primarily composed of plagioclase feldspar (calcium-rich) and pyroxene (augite and hypersthene). May also contain olivine, biotite, and hornblende.
* Diorite: Mixture of plagioclase feldspar (intermediate in calcium content) and hornblende. Can also have pyroxene (augite), biotite, and quartz (though less than granite).
2. Color:
* Granite: Often light-colored, ranging from pink to gray depending on the feldspar content.
* Gabbro: Typically dark gray to black, sometimes with greenish hues.
* Diorite: Intermediate in color, often a dark gray with patches of lighter feldspar.
3. Texture:
* Granite: Coarse-grained, with crystals typically visible to the naked eye.
* Gabbro: Coarse-grained, similar to granite in texture.
* Diorite: Can range from medium-grained to coarse-grained, sometimes with a slightly more irregular texture than granite or gabbro.
4. Chemical Composition:
* Granite: High in silica (SiO2), low in iron and magnesium.
* Gabbro: Lower in silica, higher in iron and magnesium compared to granite.
* Diorite: Intermediate in silica, iron, and magnesium content between granite and gabbro.
5. Formation:
* Granite: Forms from the cooling and crystallization of magma deep within the Earth's crust.
* Gabbro: Forms from the cooling and crystallization of magma in the Earth's crust, often associated with oceanic crust formation.
* Diorite: Forms from the cooling and crystallization of magma that has an intermediate chemical composition, often found in volcanic arcs and continental margins.
Key Differences:
* Quartz Content: Granite is the only one of the three that typically has significant quartz content.
* Feldspar Type: Granite has mostly alkali feldspar, gabbro has mostly plagioclase feldspar (calcium-rich), and diorite has a mixture of the two.
* Color: Granite is generally lighter, gabbro is generally darker, and diorite is somewhere in between.
Remember: These are general guidelines. You can also use other features, like the presence of specific minerals or the rock's overall appearance, to help you distinguish between these rocks.
