Obsidian doesn't typically form crystals. It's a volcanic glass, meaning it cools so quickly from molten lava that there isn't enough time for the atoms to arrange themselves into a crystalline structure.

Instead, obsidian often forms in amorphous shapes:

* Rounded masses: These are the most common forms, often with a smooth, glassy surface.

* Fractured shapes: Obsidian can also fracture into sharp, jagged pieces, which can be used for tools or weapons.

* Flows: Obsidian can also form flowing, ribbon-like shapes as it cools.

While some rare obsidian samples do exhibit spherulites, these are not true crystals but rather microscopic, radial arrangements of crystals.