Quartz / Common Opal

Physical Properties

Hardness: 7 (Quartz) to 5.5-6.5 (Opal); Color: Translucent white to milky; Luster: Vitreous to waxy; Crystal Structure: Trigonal (Quartz) or Amorphous (Opal); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.1 - 2.65.

Formation & Geological History

Formed from silica-rich hydrothermal fluids or groundwater circulating through rock cavities. This specimen appears to be a small nodule or vein fragment, likely from a sedimentary or volcanic environment.

Uses & Applications

Quartz is used in electronics (oscillators), optics, glass manufacturing, and construction. Common opal is used for minor lapidary work or inexpensive jewelry beads.

Geological Facts

Quartz is the second most abundant mineral in Earth's continental crust. Unlike precious opal, common opal does not show 'play of color' (opalescence) and is found in much larger quantities worldwide.

Field Identification & Locations

Identify in the field by its hardness (will scratch glass), conchoidal fracture (breaks like glass), and lack of cleavage. Often found in gravel beds or as intrusions in host rock.

Identified on: 4/20/2026

Mode: Standard