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

缟玛瑙（玉髓质黑色或黑白条带）是玛瑙（SiO2隐晶质石英的条带变种）中颜色最深的类型，以平行条带著称，典型的黑白条带玉髓被称为缟玛瑙，纯黑色无条带者通常经过染色处理（天然纯黑缟玛瑙极为罕见）。缟玛瑙的使用历史可追溯至古希腊和古罗马时代，大量用于浮雕、凹雕和印章宝石，也是维多利亚时代哀悼珠宝的标志性材料。现代珠宝中缟玛瑙以其深邃的黑色而广受喜爱，常用于男士首饰和钻石点缀设计。摩氏硬度6.5至7，化学性质稳定，耐久性好，价格亲民。