obsidian - black obsidian - teaching hand specimen
Obsidian is a volcanic glass with the composition of granite or rhyolite. Because it cooled and solidified almost instantaneously in the earliest stages of an explosive volcanic eruption, its atoms did not have enough time to fall into a regular crystalline pattern and are essentially an unorganized mass of atoms exhibiting the curved or conchoidal fracture typical of glass.
The color of obsidian is due to impurities. Black obsidian results when the impurities are hornblende, magnetite, biotite or a pyroxine. Brown obsidian forms when the impurity is hematite or limonite. Inclusions of gas or tiny inclusions of water result in a silvery reflectance that is desirable in lapidary. Brown and black are commonly swirled together in some obsidian flows.
Almost every obsidian source in North America was known to native Americans. Since obsidian from each source is geochemically distinct, the origin of the obsidian used in stone tools can be traced. Many surprisingly obscure sources, such as obsidian float in alluvium where the original flow has weathered away, were utilized for cutting tools or was collected as trading material.
Edges may be sharp if dropped by a student. You can dull them by rubbing against a hammer. We dull these before shipping, but it doesn't affect appearance.
Select a specimen: When more than one specimen is shown, you can select a particular specimen by telling us what is in the photo with it, a black and silver pen, a black mechanical pencil, a blue and silver pen, or one of those plus some number of coins, or you can let us make the selection.
Shipping: in a First Class package unless combined with other items. Click > here < for shipping rates. Use back button to return to this page.
Making multiple purchases? Click on the "combine shipping" button in the shopping cart. We'll send an invoice with combined shipping. A link in that invoice will bring you back to checkout, no hassle.