Demantoid Garnet on Matrix

Hardness: 6.5-7 on Mohs scale. Color: Vivid green to yellowish-green, often with a brilliant sparkle. Luster: Adamantine to vitreous. Crystal Structure: Isometric (typically dodecahedral or trapezohedral crystals). Often exhibits horsetail inclusions (fine, fibrous chrysotile) unique to demantoid from some localities. The matrix appears to be a light-colored, possibly feldspathic or quartz-rich rock.

Demantoid garnets are typically found in serpentine-derived rocks and regionally metamorphosed rocks, often associated with chromite and other iron-rich minerals. They form under relatively high temperatures and moderate pressures during regional metamorphism or in hydrothermal veins in serpentinized ultramafic rocks. The geological age can vary widely deepening on the specific deposit, ranging from Mesozoic to Cenozoic.

Primarily used as a gemstone in high-end jewelry due to its exceptional brilliance (higher than diamond) and vivid green color. Its rarity and beauty make it highly sought after by collectors and investors. Specimens like the one pictured, with well-formed crystals on a matrix, are particularly valued by mineral collectors.

Demantoid is one of the most valuable and rare varieties of garnet. Its name, derived from the Dutch word 'demant' meaning 'diamond', refers to its exceptional fire and dispersion, which is higher than that of diamond. The 'horsetail' inclusions, resembling a curving plume, are a unique and diagnostic feature found in demantoid from the Ural Mountains of Russia, often increasing its value and proving its natural origin.

In the field, demantoid would be identified by its distinctive vibrant green color, strong adamantine luster, and the presence of dodecahedral or trapezohedral crystal forms. Association with serpentinite or other metamorphic rocks can be an indicator. It is commonly found in Russia (Ural Mountains, historically the most famous source), Namibia, Madagascar, Italy, and Iran. For collectors, look for good crystal formation, clarity, intense color, and the presence of a natural matrix. The 'horsetail' inclusions are a key identifying feature for Russian demantoids.