Stones/Gems with O

• Obsidian

  Real volcanic glass; common semiprecious gem.

• Onyx

  Well-known banded chalcedony gemstone.

• Opalite

  Man‑made opalescent glass, sold as a gemstone

• OPAL

  Famous precious gemstone with play-of-color.

• opals

  Precious silica gemstone with play of color

• Olivine

  Real mineral; gem variety known as peridot.

• orange calcite

  Orange variety of calcite, used as a semi‑precious stone

• oval diamond

  Cut style + diamond gem, valid trade term

• Orange diamond

  Colored diamond variety, rare but real

• orange topaz

  Trade name for orange citrine/topaz, warm fiery hue

The words in the list Stones/Gems with O come from players of the word game City, Country, River.