This page brings together 12 minerals that all start with the letter O, running alphabetically from “Obsidian” to “Ozokerite.” You’ll find a mix of familiar gemstones and rare collector’s specimens here, ranging from glossy volcanic glass to delicate cotton-like crystals. People value these minerals for jewelry, carving, pigments, and everyday products like candles and polishes, while collectors prize the rarer finds.
Minerals are naturally occurring solid substances with a specific chemical makeup and an orderly internal structure. They form the basic building blocks of rocks and shape much of the world around us. Many also carry deep cultural meaning, like opal, which has been treasured as a symbol of hope and good fortune for centuries.
Below you’ll find the table with the mineral name and its description.
Mineral: The common name of each specimen, listed in alphabetical order so you can quickly scan the page and find the one you’re looking for.
Description: A short, plain-language summary that tells you what each mineral looks like, how it forms, and where you might see it used.
Minerals
Mineral
Obsidian
Okenite
Oligoclase
Olivine
Onyx
Opal
Orpiment
Orthoclase
Orthoclase Moonstone
Otavite
Ottrelite
Ozokerite
Descriptions
Obsidian
A naturally occurring volcanic glass formed when lava cools rapidly. Though not a true crystalline mineral, it is prized for its glossy black appearance and razor-sharp edges, historically used for tools and blades.
Okenite
A rare silicate mineral known for its delicate, fibrous white crystal clusters that resemble fluffy cotton balls. It often forms in the cavities of volcanic basalt rocks.
Oligoclase
A common feldspar mineral and member of the plagioclase series, usually pale and translucent. A gem variety called sunstone shows a shimmering metallic glitter from tiny inclusions.
Olivine
A green magnesium-iron silicate that is one of Earth’s most abundant minerals in the mantle. Its gem-quality form is the bright green birthstone peridot.
Onyx
A banded variety of chalcedony quartz, typically with parallel black and white layers. It has been carved into jewelry, cameos, and ornamental objects for thousands of years.
Opal
A hydrated form of silica famous for its dazzling play of color that flashes rainbow hues. It is the October birthstone and forms by deposition in rock cracks and cavities.
Orpiment
A bright orange-yellow arsenic sulfide mineral once used as a pigment and in early medicine. It is soft, toxic, and often found alongside its relative realgar.
Orthoclase
A pink-to-white potassium feldspar that is a key rock-forming mineral in granite. Its transparent yellow gem variety is known as moonstone or noble orthoclase.
Orthoclase Moonstone
A gem variety of orthoclase feldspar displaying a floating blue-white sheen called adularescence. It is widely used in jewelry and associated with mystery and intuition.
Otavite
A rare cadmium carbonate mineral, typically forming small white to yellowish crystals. It was first discovered near Otavi in Namibia, from which it takes its name.
Ottrelite
A dark, brittle silicate mineral related to chloritoid, usually appearing as tiny greenish to black platy crystals embedded in metamorphic schist rocks.
Ozokerite
A naturally occurring mineral wax made of hydrocarbons, ranging from yellow to brown. Historically refined into ceresin wax for candles, polishes, and electrical insulation.
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