mineral

Fire Agate (Crackle Agate)

Silicon Dioxide (SiO2) - Cryptocrystalline Quartz

Hardness: 6.5-7 Mohs; Color: Gray, blue, and white with dark inclusions and crackled patterns; Luster: Vitreous to waxy; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.60-2.65

Hardness: 6
Luster: Vitreous to waxy

Identified May 22, 2026More mineral →

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Physical properties

Formation & geological history

Formed in volcanic and sedimentary rocks where silica-rich groundwater fills cavities and fissures over millions of years. This specific crackled appearance is often achieved via thermal shock (heat treating and rapid cooling) of natural agate.

Uses & applications

Primarily used in jewelry for beads, cabochons, and decorative items. It is highly valued in the 'New Age' crystal market for its aesthetics.

Geological facts

Natural agate has been used by humans for over 3,000 years for seals and jewelry. The 'crackle' effect is a popular modification that highlights the internal grain structure of the stone.

Field identification & locations

Identify in the field by its hardness (will scratch glass) and waxy luster. Common locations for natural agate include Brazil, Uruguay, and the Southwestern United States (Arizona/Mexico for true fire agate). Look for botryoidal or banded habits in volcanic outcrops.

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