Onyx

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A layered variety of chalcedony banded in parallel black and white, onyx also lends its name to uniformly black chalcedony when used as a gem. It forms in the cavities of volcanic rocks and in sedimentary silica deposits, most notably in India, Brazil, Uruguay, and the United States. Belonging to the trigonal quartz group, it measures 6.5 to 7.0 on the Mohs scale. Since antiquity the stone's contrasting layers have been exploited for cameos, intaglios, beads, and large decorative objects, while pure black onyx became popular in mourning and men's jewelry. A moderately priced semi-precious stone, onyx is traditionally associated with February.

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 of Onyx shown against the ten reference minerals, from talc (1) to diamond (10).

Mohs	Reference mineral	Onyx
1	Talc
2	Gypsum
3	Calcite
4	Fluorite
5	Apatite
6	Orthoclase
7	Quartz	●
8	Topaz
9	Corundum
10	Diamond

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

Ónix é uma variedade de calcedónia com bandas paralelas alternadas, tipicamente pretas e brancas. A variedade mais valorizada em joalharia é o ónix preto, muitas vezes material de calcedónia tingido de preto. Historicamente, o ónix foi usado em camafeus, intaglhos e joalharia de luto vitoriana. A sua dureza e solidez tornam-no ideal para escultura detalhada. O nome deriva do grego para garra ou unha. Os principais depósitos encontram-se no Brasil, Índia, Uruguai e Madagascar. O ónix preto é atualmente um dos materiais de joalharia mais populares em design contemporâneo.