OK, I'll assume the role of GOSA mineralogist and answer Pat's question.  Olivine is not really greenish black, but can be brownish-green when containing significant iron.  Typically it is  yellowish-green.  Gem quality olivine is known in the gem trade as peridot. 
Strictly speaking, olivine and garnet are actually names of mineral groups.  The most common minerals of the olivine group are forsterite (magnesium end member) and fayalite (iron end member), which form a complete solid solution series between the end members.
Some of the more well known minerals of the garnet group include almandine, pyrope, grossular, andradite, and spessartine.  Of these, andradite commonly occurs in darker shades of brown and black.  The others are commonly used in the gem trade and tend to be more colorful (reds, oranges, pinks).
-- Will
 
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Some really nice black or silver minerals are
Galena
Hornblende
Graphite
Hematite
Stephanite

Also, garnets can be many colors--maybe Garnet Geyser? And Almandine,  
they are dark brown to black minerals.

Also, Black Pearl
Abalone
Mother of Pearl

And olivine can be greenish black, right?

I like Graphite Geyser or Black Pearl Geyser.

Just some ideas.
Pat Snyder

