Peridot

It cracks in a steam cleaner.

Olivine from the earth's mantle, brought up in basalt and occasionally arriving from space inside a pallasite meteorite. The Egyptians mined it on Zabargad in the Red Sea and called it the gem of the sun. It cracks in a steam cleaner. Warm water and a cloth is the whole procedure.

One colour only, which is unusual.

One colour only, which is unusual, and the yellow-green tone is diagnostic among green gems. Egyptians mined it on Zabargad in the Red Sea and called it the gem of the sun, and medieval Europe confused it with emerald for centuries. Sudden temperature change cracks it.

The back facets appear doubled when you look through.

Look through a faceted one at the back edges and they appear doubled, because peridot refracts light twice. It is mantle olivine carried up in basalt, and some of it arrives inside pallasite meteorites instead. Medieval Europe kept confusing it with emerald for centuries.

One colour, no exceptions, and an oily rather than glassy shine.

It occurs in one colour and one only, a yellow-green with an oily rather than glassy shine. Olivine from the mantle, carried up in basalt, and occasionally arriving inside a meteorite instead. Classical and medieval sources say it kept nightmares off, which is a very old job for a stone.

The Egyptians mined it and called it the gem of the sun.

The Egyptians mined it on Zabargad in the Red Sea and called it the gem of the sun. It rides up from the mantle in basalt, and some of it arrives from space inside pallasite meteorites. One colour only, always with yellow in it, never blue.

Lily-pad inclusions around a dark speck, nearly unique to peridot.

Olivine from the mantle, delivered upward by basalt, and occasionally arriving from space inside pallasite meteorites. Look through a cut stone at the back facet edges and they appear doubled, because the birefringence is strong enough to see unaided. Lily-pad inclusions around a dark speck are nearly unique to it.

It occurs in one colour and offers no alternatives.

Olivine from the mantle, and one of very few gems that occurs in a single colour, always with yellow in it and never with blue. Look through a faceted stone and the back facet edges appear doubled, because peridot splits light hard. The lily-pad inclusions are close to unique.

It came up from the mantle inside the basalt.

Olivine from the mantle, carried up inside basalt and occasionally arriving from space inside pallasite meteorites. The Egyptians mined it on Zabargad in the Red Sea and called it the gem of the sun. Classical and medieval sources credit it with keeping off nightmares and envy.

Occasionally it arrives from space inside pallasite meteorites.

Olivine from the earth's mantle, brought up in basalt, and occasionally arriving from space inside pallasite meteorites. The Egyptians mined it on Zabargad in the Red Sea and called it the gem of the sun, and medieval Europe spent centuries confusing it with emerald. Lily-pad inclusions confirm it.

Mantle rock, carried up in basalt or delivered by meteorite.

Olivine from the earth's mantle, carried up in basalt and occasionally delivered inside a meteorite. It occurs in exactly one colour, always with yellow in it, and the small lily-pad fractures around a dark speck are close to unique. Egypt mined it on Zabargad in the Red Sea.

One of very few gems that occurs in a single colour.

Olivine, brought up from the mantle in basalt, and occasionally arriving from space inside pallasite meteorites. It is one of very few gems that occurs in a single colour, so there is no variety to choose from. Egypt mined it on an island in the Red Sea and called it the gem of the sun.

One of the few attributions here that is genuinely old.

Classical and medieval sources credit it with keeping nightmares off, which is one of the few attributions here that is genuinely old. The mineral is olivine, from the mantle, carried up in basalt and occasionally arriving inside meteorites. It cracks in a steam cleaner.

Peridot is carried for abundance, self-love and protection. Olivine from the earth's mantle, brought up in basalt, and occasionally arriving from space inside pallasite meteorites.. Tradition links it to the heart, solar-plexus chakra.

Peridot is not faked often, but it is still worth checking. Yellow-green with an oily luster plus visible facet doubling. Lily-pad inclusions under 10x confirm it.. Rarely treated; occasional fracture filling on heavily included material.

A short rinse is fine for peridot, then dry it.