Cobalt Blue Obsidian

Cobalt Blue Obsidian is a vivid blue glass marketed within the colored-obsidian range. Natural obsidian does not occur in a transparent cobalt blue; the few genuinely bluish natural pieces owe their look to a faint surface sheen, not body color.

This material is manufactured glass colored with cobalt oxide, the classic colorant for deep blue glass. It may also be labeled obsidianite or art glass.

It is an inexpensive, attractive ornamental product rather than a natural mineral.

Obsidian forms naturally when felsic lava cools too fast for crystals to grow, producing amorphous glass colored only by iron, magnesium, and tiny mineral inclusions.

Cobalt blue material is made in a furnace by adding cobalt oxide to a silica melt, a method used for blue glass for millennia. The result is a uniform, intensely blue glass whose evenness and clarity, plus internal bubbles, mark it as manufactured rather than volcanic.

Color: Deep, even cobalt blue, typically translucent and bright.

Luster: Vitreous; conchoidal fracture.

Hardness: ~5-6.

Streak: White.

Look-alikes: Lapis lazuli and sodalite are opaque, blue, and stony (lapis often with pyrite flecks). Blue chalcedony is waxy. Cobalt blue obsidian is unmistakably glassy and translucent, with bubbles and swirls visible under a loupe.

Cobalt Blue Obsidian is used for decorative tumbles, beads, spheres, and pendants, and for inexpensive jewelry. Its rich blue is popular in crystal displays.

Metaphysical sellers tie it to intuition, the third eye, and communication, associations from folklore rather than mineralogy. As manufactured glass it has decorative value only.

Buyers wanting natural blue-toned obsidian should look for genuine blue-sheen obsidian, where the blue is a surface optical effect, not a body color.