Obsidian is an igneous rock that has an amorphous structure. It is produced from rhyolite that is rich in silica and low in water. When this ryolith erupted, its temperature quickly drops below the temperature to create mineral crystals and a natural silica glass was formed.
Black is the most abundant color in obsidian, and it is derived from oxidized magnetite contained within the silica. The presence of Hematite creates a red color.
Patterns of gas bubbles can create sheens within the glass. When they are combined with oxides, they can produce an internal gloss, such as silver obsidian or an iridescence like rainbow obsidian. If these iridiscent layers are heavily faulted the variety of “Velvet-Obsidian” can be developed.
I´am sorry, but a more exact point of mining than “Chihuahua” could not be determined for this gem stone material so far from me.