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Elahera green chalcedony vs chrome tourmaline: refractive index and specific gravity?

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Elena Chalcedony•905 rep

How do gemmologists in field purchasing offices distinguish apple-green nickeliferous chrysoprase from fine chrome tourmaline in alluvial gravel parcels?

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✓Accepted Answer

Differentiating cryptocrystalline quartz (chrysoprase) from crystalline chrome tourmaline relies on fundamental physical and optical constants. Chrysoprase (colored by nickel silicates) is aggregate chalcedony, displaying an aggregate reaction in the polariscope, a flat refractive index of 1.530 to 1.540, and a lower specific gravity of 2.58 to 2.64. Chrome tourmaline (colored by chromium and vanadium) is singly monocrystalline, showing strong dichroism (dark emerald-green to yellowish-green) under a calcite dichroscope, a higher refractive index (1.624 to 1.644), and a specific gravity of 3.05 to 3.12.

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D
Dr Kularatne Gem•1950 rep

Under a Chelsea color filter, chrome tourmaline glows bright red due to strong chromium transmission windows, whereas nickel chrysoprase remains inert green.

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Elena Chalcedony•905 rep

Chrysoprase exhibits a waxy to greasy luster on unpolished rough fracture surfaces, distinct from the vitreous, bright glassy fracture surfaces of tourmaline.

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Dr Bandula GSMB•1850 rep

Tourmaline crystals feature rounded triangular cross-sections with heavy vertical striations along prism faces, whereas chrysoprase forms botryoidal nodular masses.

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Guru Dharmasena Wood•1830 rep

Specific gravity immersion testing using bromoform (SG 2.85) separates them instantly: chrysoprase floats on the surface while dense tourmaline sinks.

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Dr Dayaratne Spices•1820 rep

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