* Abundance Varies: Rock type abundance depends on where you're looking. The Earth's crust is mostly made of igneous rocks, but the mantle is mostly peridotite, an ultramafic igneous rock.
* Classification is Subjective: There are many ways to classify rocks, and depending on the system, certain rock types might be lumped together or split into multiple categories.
* Relative vs. Absolute: It's easier to say which rock types are relatively uncommon compared to others like granite, basalt, and sandstone, rather than determining their absolute rarity.
However, some rock types considered relatively uncommon include:
* Kimberlite: This ultramafic igneous rock is known for being the source of diamonds.
* Anorthosite: A plutonic rock composed primarily of plagioclase feldspar. It's found in the lunar highlands but is rare on Earth.
* Eclogite: A metamorphic rock formed under very high pressure and temperature, typically found in the Earth's mantle.
Other relatively uncommon rock types:
* Carbonatite: A rare igneous rock rich in carbonate minerals.
* Komatiite: An ultramafic volcanic rock, rarely found today but more common in the Archean eon.
* Blue Schist: A metamorphic rock formed under high pressure and relatively low temperature, indicating subduction zones.
Remember, the rarity of a rock type can depend on location and geological processes, making a definitive "top three" difficult to establish.
