Demantoid is the green gemstone variety of the mineral andradite, a member of the garnet group of minerals. Demantoid is by far the rarest and most valuable member, In fact demantoid is one of the rarest of all coloured gemstones. Particularly fine Demantoids can command thousands of pounds per carat. Andradite is a calcium and iron rich garnet. Demantoids often contain radiating needle inclusions that are termed “horsetails”. Ferric iron is the cause of the yellow in the stone.
Stock Sizes: A selection of specimen stones are available in Round, Oval and Cushion cut.
Chemical Formula: Ca3 Fe2 Si3 O12
Crystal Structure: Cubic
Colour: Light to dark green and yellowish green
Hardness: 6.5-7 on Moh`s scale
Refractive Index: 1.880 – 1.889
Specific Gravity: 2.58–2.643.84
Treatments: Demantoid garnets can be subjected to heat treatment in order to enhance their colour. Such treatment is believed to be performed at relatively low temperatures and is thought not to be detectable by gemological testing. The resulting stones are stable under normal wearing conditions.
Care: Ultrasonic cleaning is generally safe, but risky if the gem contains liquid inclusions. Steaming is not recommended. The best way to care for demantoid garnet is to clean it with warm, soapy water. Avoid exposing it to heat or acids.