Rock Stars : Smoky Quartz & Feldspar

Yellowhammer's guide to Favourite Minerals.

Quartz is the second-most-abundant mineral in the Earth's Continental crust, after Feldspar.*

Smoky quartz is a brown to black variety.

Like other quartz gems, it is a silicon dioxide crystal. The smoky colour results from free silicon.

Silicate minerals all contain silicon and oxygen. 

Chrysocolla [above] is a hydrated copper silicate mineral.

 

Minerals range in composition from pure elements and simple salts to very complex silicates with thousands of known forms.

By comparison, a rock is an aggregate of minerals, and does not have a specific chemical composition. 

* Feldspars are a group of rock-forming minerals which make up as much as 60% of the Earth's crust.

Feldspar is derived from the German Feld, "field", and Spath, "a rock that does not contain ore".

Feldspars crystallize from magma in rocks, as veins. 

Rock formed almost entirely of feldspar is known as anorthosite. [below]

Summary

Minerals are composed of salts and silicates, of fixed chemical composition.

Feldpsar and quartz are two most common minerals in crust.

Chrysocolla and Quartz are examples of silicon based minerals (silcates).

Rock is a group of minerals, Feldspar mineral veins (crystallized magma) run through 60% of Earth's crust.

Anthorosite is a Feldspar rock.