Coral
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Secreted as a hard skeleton by marine polyps of the order Gorgonacea, precious coral is an organic gem built of calcium carbonate and carved into beads, cameos, and figurines since ancient times. The most prized ox-blood or Moro coral from the Mediterranean and Japanese seas shows a deep, saturated red long treasured in Chinese, Tibetan, Italian, and Native American traditions. Soft by mineral standards at 3.0 to 4.0 on the Mohs scale, it nonetheless takes a fine polish. A budget-tier organic gem, precious coral has grown increasingly rare and regulated as overharvesting and habitat loss brought many species under protection.
Physical & Optical Properties
Category
Organic Gems
Mohs Hardness
3.0 – 4.0
Specific Gravity
2.6 – 2.7
Refractive Index
1.486 – 1.658
Crystal System
Trigonal
Cleavage
None
Color
various
Birefringence
0.16
Pleochroism
Absent
Mohs Hardness
| Mohs | Reference mineral | Coral |
|---|---|---|
| 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
Budget (< $50/ct)
Where to Buy Coral
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Treatments
Dyed: mostly with polymer treatment, color and resin concentration in fractures, cavities and branches junctions. Hot point test (acetone test in some cases) may reveal the treatment. Dyed pink to red from white variety: color dignostic if from "bamboo" type (natural color is white to brownish). Dyed blue from grayish: commonly with resin treatment: light blue color concentration in pits and cracks - Blue Chart Gem Identification, Herve Nicolas Lazzarelli, 2010, p 9
Artificial pressed product (ceramics) consisting of calcite - Red; opaque; RI 1.486 - 1.658; Birefringence 0.172; Uniaxial/-; SG 2.60 - 2.70; Hardness 3.5 - 4; Trigonal. - Gemmological Tables, Ulrich Henn and Claudio C. Milisenda, 2004, p 3
3 to 4Walter Schumann, Gemstones of the world (2001) More from other references
2.60 to 2.70Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
BrittleWalter Schumann, Gemstones of the world (2001)
NoneWalter Schumann, Gemstones of the world (2001)
Irregular,SplinteryWalter Schumann, Gemstones of the world (2001)
1.486 to 1.658Walter Schumann, Gemstones of the world (2001) White and redMore from other references
Uniaxial/-Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
0.160 to 0.172Walter Schumann, Gemstones of the world (2001) White and redMore from other references
AbsentWalter Schumann, Gemstones of the world (2001)
NoneWalter Schumann, Gemstones of the world (2001)
Red, pink, white, orange, blue, brownUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Translucent,OpaqueWalter Schumann, Gemstones of the world (2001) More from other references
Dull purplish-redHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
TrigonalUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Distinctive wavy parallel fibrous structureHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Coral information at mindat.org
About Coral
宝石珊瑚（コーラル）は、ゴルゴニア目の海洋ポリプが分泌する硬い炭酸カルシウム骨格から作られ、珊瑚細工・ビーズ・彫刻品として古来から珍重されています。地中海の赤珊瑚（モモ）・ハワイの深海珊瑚・アンジェルスキン珊瑚などの変種があります。天然珊瑚は国際保護の対象となっているため現在は取引規制があります。
Compare With
On this page
Jewelry Use
Durability
2/10
Science FYI Family
Frequently Asked Questions
What is Coral?
宝石珊瑚（コーラル）は、ゴルゴニア目の海洋ポリプが分泌する硬い炭酸カルシウム骨格から作られ、珊瑚細工・ビーズ・彫刻品として古来から珍重されています。地中海の赤珊瑚（モモ）・ハワイの深海珊瑚・アンジェルスキン珊瑚などの変種があります。天然珊瑚は国際保護の対象となっているため現在は取引規制があります。
What is the hardness of Coral?
Coral has a Mohs hardness of 3.0 to 4.0, making it relatively soft for use in jewelry.
What color is Coral?
Coral is primarily Various.
How much does Coral cost?
Coral falls into the Budget (< $50/ct) price range. Prices vary based on color, clarity, cut, and origin.
What is the crystal system of Coral?
Coral belongs to the Trigonal crystal system.