Onyx

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Physical & Optical Properties

Category Semi-Precious Gems

Mohs Hardness 6,5 – 7,0

Specific Gravity 2,55 – 2,7

Refractive Index 1,53 – 1,543

Crystal System Trigonal

Color black

Mohs Hardness

Mohs Hardness: 6,5 – 7,0

1 Soft10 Hard

Crystal System

Value & Market

Price Tier Moderate ($50-500/ct)

Where to Buy Onyx

Blue Nile Fine jewelry retailer

James Allen Gemstone jewelry

Brilliant Earth Ethically sourced gems

Amazon Wide selection

Links may earn a commission at no extra cost to you.

Cultural Significance

Birthstone Month 2 (alternative)

Treatments

Black chalcedony ("onyx") is assumed to be dyed - Blue Chart Gem Identification, Herve Nicolas Lazzarelli, 2010, p 7 6.5 to 7Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references 2.55 to 2.70Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) 1.530 to 1.543Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) Uniaxial/+Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) Straight color bands (black with white layer)Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references OpaqueHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references TrigonalUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) Onyx information at mindat.org

About Onyx

Onyx is a layered variety of chalcedony (banded microcrystalline quartz) distinguished by its parallel bands of black and white, though the term also refers to uniformly black chalcedony when used as a gemstone material. It forms in the vesicles of volcanic rocks and in sedimentary silica deposits, most notably in India, Brazil, Uruguay, and the United States. Since ancient times, onyx has been carved into cameos, intaglios, beads, and large decorative objects, exploiting the contrast of its black and white layers, with pure black onyx popular in mourning and men's jewelry.