3.5" Polished Rainbow Obsidian - Mexico

Rainbow obsidian originates from rapidly cooled felsic lava flows and is most famously found in Jalisco, Mexico, though it also occurs in other volcanic regions, including the United States (like the Sierra Nevada region of California) and Japan. Its unique rainbow iridescence is caused by thin-film interference, resulting from microscopic magnetite nanoparticles or crystal inclusions that reflect light.

Obsidian is a natural volcanic "glass" that is formed when molten rock cools so quickly that the atoms don't have enough time to arrange themselves into crystals. To form obsidian, the composition of the lava must be high in silica. Depending on the minerals present within this lava along with the cooling rate, a variety of colorful bands, spots, or swirls can appear once the lava has solidified. Pure obsidian is often a solid black color, but impurities can result in small color variations throughout like those seen in rainbow obsidian.

Obsidian was an important material for many ancient people. It was used for making tools, weapons, jewelry, and decorative items. It was a major barter material for Native Americans. Its conchoidal fracturing creates extremely sharp edges when it is broken, which made it ideal for making knives, scrapers, arrowheads, and spearpoints. It is even occasionally used today to produce surgical scalpels, since the edges can be several times sharper (only 3 nanometers wide) than blades produced from steel.