Black Agate
Black Chalcedony
A variety of Chalcedony
What is Black Agate?
Black Agate is a type of microcrystalline quartz that is opaque and appears black or dark gray in color. However, the gemstone of black Agate in the market is usually created by suffusing chalcedony in a sugar solution and then treating with sulfuric acid, causing the stone's appearance to change to a black color. This process enhances the stone's appearance, making it very popular. It is commonly used as a Jet imitation.
Optical Properties
- Refractive Index
- 1.530-1.543
- Birefringence
- 0.003-0.009
- Pleochroism
- None
- Optical Character
- Biaxial positive
- Dispersion
- 0.013
Discover Values
Black Agate Market Value Calculator
Estimate the market value of Black Agate using size, quality, and finish. This preview calculator is for quick context and is not a formal appraisal.
Black Agate Localities Map
See where Black Agate is found with a localities map, collecting zones, and geology context. Generate a sample map preview below.
Health & Safety Information
- ⚠️Harm Reason: Black Agate in powdered form can be toxic due to its Crystalline Silica content.
- ⚠️Physical Toxicity: Quartz, silica, crystalline silica and flint are non-toxic materials, but very fine dust containing quartz, known as respirable crystalline silicon (RCS), can cause serious and fatal lung disease. Lapidaries should exercise caution when cutting silica.
- ⚠️How to prevent the risks of Black Agate?
Quick Facts
Physical Properties
- Color
- Black
- Hardness (Mohs)
- 6.5 - 7
- Density
- 2.55 - 2.7 g/cm³
- Streak
- White
- Luster
- Vitreous, Waxy
- Crystal System
- Trigonal
Chemical Properties
- Chemical Formula
- SiO2
- Elements
- O, Si
Also Known As
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