Peridot

Peridot is one of the few gemstones that occur in only one color, an olive green and is a Magnesium Iron Silicate. The intensity and tint of the green  depends on how much iron is contained in the crystal structure, so the color of individual peridot gems can vary from yellow to olive to brownish-green. The most valued color is a dark olive-green. Peridot are often mistaken for Emeralds which look quite similar.

Peridot crystals have been collected from some Pallasite meteorites (A type of stony/iron meteor).

Peridot rates as 6.5 to 7.0 on the Mohs hardness  scale and some examples are shown below.