We know that throughout history various civilizations and groups have forged weaponry from bronze, iron and steel. I recall that the Aztecs used an obsidian blade in combat (or rather, the sword used obsidian in its making), and I was curious if other civilizations created weapons from "exotic" or unusual materials.
Are the Aztecs the only group to have used obsidian? Have other other tribes or civilizations used other materials or metals in weapon making?
Before the discovery that tin could be added to copper to create bronze, there was a period known as the copper age. I'm finding it surprisingly difficult to find good sources backing this up, but it appears there have been some finds of swords made from worked copper.
It would certainly be possible for a skilled artisan to craft a sword from knappable stones such as obsidian or flint. However, it is not very sensible. The trouble with stone is that it is extremely hard, and as a result, extremely brittle. When a torsional force is applied to stone (bending force), it cannot bend, it can only shatter. A shattered sword is pretty catastrophic in a battle senario.
Instead, other weapons are much more sensible with such a hard substance, namely spears and axes. And that is what archaeologists see. Stone knives exist, and are common finds at stone-age digs; but these are considered tools for things like skinning and butchering animals, not as weapons of war. As far as aztec weapons, the South American combat weapon with which I am familiar is a sort of a cross between a club and an axe. The weight comes from a heavy mass of wood at the end of the club, and it is tipped with a small sliver of a blade. Experimental archaeologists working with reproductions found that they blade could and did crack in combat, but they felt confident that the weapon could still be deadly as a bashing weapon without it.
As far as other materials for making swords, well, we have accounts from swordsmanship primers verifying that practice swords have been made from wood at least since the 16th century, and probably quite a long while before that. But again, these are intentionally made to be nonfatal.
In modern times, swords have been made from plastics and composite materials like fiberglass or carbon fiber. But once again, these are not intended for true combat.
for materials for bladed or pointed combat weapons that aren't swords, materials have included bone, pointed fire-hardened wood, antler, ivory, tooth, I think seashell (could be mistaken), and brass (copper + zinc). Brass blades would not be common as serious weapons any time tin was available. A number of brass weapons are ceremonial.