Chocolate Opal - reddish-brown variety of Noble Opal.
 
 
From: Mezezo, Shewa Norte, Amhara Region, Ethiopia.
 
 
Opal with 7,4 grams (37 carats) and 2,5 x 2,0 x 1,8cm.
 
 
Chocolate Opal is an extremely rare and iconic variety of Noble Opal, famous for its chocolate-brown background color. It is mined exclusively in the Mezezo opal field on the Yita Ridge volcanic ridge. Unlike Australian (sedimentary) opals, these opals formed in cavities within volcanic rocks, specifically Rhyolites.