The gorgeous black rutile quartz gemstone cabochon shown here is 24mm long. It was mined in Brazil. 

Rutile quartz is thought to act as an antidepressant. It is believed to relieve fears, phobias and anxiety. It is supposed to absorb mercury in cases of poisoning. It is thought to assist with impotence and infertility and help with exhaustion. Rutile quartz is thought to assist with issues of the respiratory tract and thyroid.

I used this cabochon to create this custom piece: