Agate is a form of chalcedony (a variety of microcrystalline quartz). It occurs in nodular masses in rocks such as volcanic lavas. When split open, it reveals an amazing variety of colors and patterns. It has a distinct banding that distinguishes agate from other kinds of chalcedony (like onyx, sard, and sardonyx). Band colors are determined by the differing impurities present.
Since agate is porous, it is often dyed to enhance the natural color. It occurs in several different forms. The stone is often collected and polished by enthusiasts. It is formed in cavities in volcanic rocks. The silica-rich fluids give colors to their bands. Agatized wood is fossilized wood that has had its organic matter replaced by agate.
Agate is a very popular stone for carving and polishing. It is also used in making bowls, cups, spoons, and forks.
Occurrence
The most popular area for agates is Idar-Oberstein in Germany. There, the agate has been collected since 1548. It now imports agates from the huge deposits in Brazil and Uruguay. Moss agate also occurs in Pakistan, China, India, and the USA. The most famous agatized wood is in the Petrified Forest in Arizona (USA). Agate is also found in Madagascar, Mexico, Egypt, Italy, and Scotland.
Agate Properties
- Specific Gravity: 2.61
- Refractive Index: 1.53-1.54
- Birefringence (DR): 0.004
- Luster: Vitreous
- Crystal Structure: Trigonal
- Composition: Silicon dioxide
- Hardness: 7
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