sedimentary
Blue Chalcedony Agate Slice
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Banded light blue, white, and translucent gray; Luster: Waxy to vitreous; Crystal structure: Trigonal/Monoclinic; Cleavage: None; Specific Gravity: 2.58-2.64
- Hardness
- 6
- Color
- Banded light blue, white, and translucent gray
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 Mohs; Color: Banded light blue, white, and translucent gray; Luster: Waxy to vitreous; Crystal structure: Trigonal/Monoclinic; Cleavage: None; Specific Gravity: 2.58-2.64
Formation & geological history
Formed by the deposition of silica from groundwater in the cavities of igneous rocks or sedimentary formations. This specific piece shows concentric banding characteristic of a geode filling.
Uses & applications
Used primarily for ornamental purposes, jewelry, lapidary art, and as a healing crystal in alternative medicine. Slices are often used as coasters or display pieces.
Geological facts
Agate was named by Theophrastus, a Greek philosopher, who discovered the stone along the shore line of the Dirillo River in Sicily. The blue color often comes from light scattering (Tyndall effect) through the tiny quartz crystals.
Field identification & locations
Identifiable by its distinct concentric banding and waxy texture. Commonly found in volcanic regions of Brazil, Uruguay, and the United States. In the field, look for nodules with a rough, weathered exterior.
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