Olivine (likely Peridot variety)

Hardness: 6.5-7 (Mohs scale); Color: Typically olive green, but can be brownish-green, yellow-green, or reddish-brown; Luster: Vitreous (glassy) to greasy; Crystal Structure: Orthorhombic; Cleavage: Poor in two directions; Specific Gravity: 3.2-4.4

Olivine is a common mineral in mafic and ultramafic igneous rocks such as basalt, gabbro, dunite, and peridotite. It crystallizes at high temperatures from magnesium-rich and iron-rich magma. Peridot, the gem variety, forms deep within the Earth's mantle and is brought to the surface by volcanic activity. Geological age varies depending on the specific igneous event.

Primarily used as a gemstone (Peridot) for jewelry. Lower-grade olivine is used in industry as a refractory material, in sandblasting, and as a source of magnesium. It has also been explored for CO2 sequestration due to its chemical reactivity.

Peridot is the gem-quality variety of olivine. It is one of the few gemstones that occurs in only one color: green. Peridot can be found in solidified lava and in peridotite xenoliths brought to the surface by volcanoes. Some peridot has extraterrestrial origins, found in pallasite meteorites.

In the field, olivine can be identified by its distinctive olive-green color, glassy luster, and conchoidal fracture. It is a relatively heavy mineral. It won't scratch quartz. Common locations include volcanic areas, especially basaltic lava flows and peridotite intrusions worldwide. Notable sources for gem-quality peridot include Arizona (USA), Pakistan, China, Vietnam, and Myanmar. For collectors, look for specimens with good crystal form, vibrant color, and transparency.