Gold

Hardness: 2.5–3 on Mohs scale; Color: Golden yellow to brassy yellow; Luster: Metallic; Crystal Structure: Isometric (cubic); Cleavage: None; Specific Gravity: 19.3 (very high)

Formed primarily in hydrothermal quartz veins and as secondary deposits in alluvial (placer) environments. It can be found in rocks from the Precambrian era to more recent eras following tectonic activity.

Used extensively in jewelry, electronics (due to high conductivity and corrosion resistance), finance (gold bullion), and dentistry.

Gold is so malleable that a single ounce can be beaten into a sheet covering 100 square feet. It is one of the least reactive chemical elements and is solid under standard conditions.

Identify by its high density, metallic luster, and sectility (can be cut with a knife without crumbling). Unlike pyrite, it is soft and will dent rather than shatter. Commonly found in stream beds and mountainous regions of California, Alaska, and Australia.