Fortification agate is a form of chalcedony (a variety of microcrystalline quartz). It occurs in nodular masses in rocks such as volcanic lavas. Fortification agate has angularly arranged bands resembling an aerial view of a fortress. When magnified, bands in the fortification agate resemble hill forts. The rough of the stone has colorless quartz crystals with an arrangement of colored bands due to iron oxides and hydroxides.
Occurrence
The most popular area for fortification agate is Idar-Oberstein in Germany. There, the fortification agate has been collected since 1548. It now imports fortification agate from the huge deposits in Brazil and Uruguay. Fortification agate also occurs in Pakistan, China, India, and the USA.
Fortification 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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