This piezoelectric mineral can be found at the bottom of Bowen's reaction series, and this second most common mineral in the world after Feldspar also comes in "smoky" and amethyst varieties.
Despite their name, Herkimer diamonds are actually composed of a double terminated type of this mineral. When subject to extreme heat, this mineral can be artificially transformed into the mineral citrine, and this mineral can keep an electronic rhythm when mechanical stress is applied to it. This piezoelectric mineral can be found at the bottom of Bowen's reaction series, and this second most common mineral in the world after Feldspar also comes in "smoky" and amethyst varieties. For 10 points, name this mineral that has a Mohs hardness of 7 and has the chemical formula SiO2.
Despite their name, Herkimer diamonds are actually composed of a double terminated type of this mineral.
Quartz