The Indians of the west found lumps and layers of glossy, black obsidian around their volcanoes and lava flows. They found that they could chip it away in fragments to form a sharp, hard cutting edge and obsidian was a treasured mineral for making arrowheads and hunting knives. The western Indians may have traded their native obsidian with Indians in other parts of the country .. where the beautiful mineral is not to be found.

 A lump of granite is gritty and sturdy enough to endure through the ages. A lump of pumice is pale and light and frothy with frozen foam. A lump of obsidian is black and glossy and, though as hard as granite, it has a very short life span in the world of rocks. With all their differences, these minerals are related to each other. For all are made from the same chemical elements and they were formed by the same upheavals in the earthts crust.

All of them are formed in the seething fury of volcanic activity. Their story begins deep underground when rocks and minerals, gases and steamy vapor boil together to form a pool of buried magma. From time to time, the buried kettle boils over, a volcano erupts and the magma comes pouring up towards the surface. Some is buried in pockets and byways on the way to the top. Some streams forth in rivers of molten lava.

The condition of the lava depends to some extent upon the eruption. It may be a slow, gentle oozing or a seething river soon buried under a new flow from the furious volcano. Lava exposed to the air may cool fast. Buried lava may not cool for many centuries. Foamy bubbles of gas may be trapped in the cooling rock, as happens in pumice, or driven off as in granite and obsidian.

These rocks are called igneous, or fire formed. Those, like obsidian, which cool on the surface are called extrusive igneous rocks. Obsidian cooled too fast for its chemicals to form crystals. However, in some¬samples, gritty crystals may be seen inside the glassy rock and the sides may be seamed with streaks of rough crystals.

Obsidian contains a large proportion of silica which is made from the elements oxygen and silicon. It is rated in class six on the mineral scale of hardness, which makes it as hard as common feldspar. Obsidian, for a rock, has a very short life span for it is easily altered by water and weather. When we find it, we know that we are in a region of recent volcanic activity. It was made, perhaps, a few million years ago.

 Rainbow obsidian glows with buried colors of green, grey or violet and other varieties are tinged with green or brown. A thin slice of any obsidian is clear as glass and when a lurap is broken, it forms an uneven fracture. The new surface forms curved hollows, rippled like delicate shells. For this reason we say that obsidian has a conchoidal – or shell like fracture.