SciShow Rocks Box: Emerald

Location: Bahia, Brazil Formula: Be3Al2(SiO3)6 Mohs Hardness Scale: 7.5-8 Humans like shiny gems, and one of our favorites are emeralds. Just like this one! But technically, emeralds shouldn’t be possible. These crystals only form when beryllium, found in the highest level of the Earth’s crust, gets mixed up with chromium and vanadium, both of which only come from the Earth’s mantle. How do these unlikely elemental friends meet? Deep deposits of ultramafic bedrock are pushed up from the mantle over the course of billions of years, and then magma that contains beryllium has to squish its way through the bedrock. The emeralds form when the chromium and vanadium meet that beryllium, in a thin zone around the magma intrusion. It’s a one-in-a-million process that gives us these unique and lovely gems.