The metal is expensive, not because it is rare but because of the expense to produce and work it. The minerals mined for titanium are all oxides, unlike many base metals that are mostly mined as sulfide minerals.

Black diamonds, also known as carbonado, are extremely rare, and are found naturally only in Brazil and Central Africa. The cosmic origin theory is based on their carbon isotopes and high hydrogen content.

Watching for these areas is one of my primary targets during the winter. It doesn’t take but a few inches of the surface moving away to give a fantastic target response that you didn’t hear prior to the washing of the surface.

The old timers typically washed these areas down to bedrock, and some areas appear terraced. I would imagine this is because these hydraulic mines were generally where the miners found old Tertiary river channels on the sides of mountains that were gold-bearing.