sedimentary
Quartz (Chert/Chalcedony variety)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Creamy white with tan/brown surface staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Creamy white with tan/brown surface staining
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Creamy white with tan/brown surface staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed by the accumulation of microcrystalline silica in sedimentary environments or as secondary infilling in volcanic rock cavities. Common in the limestone and volcanic terrains of East Java.
Uses & applications
Primarily collected as a decorative stone. Tough varieties were historically used for stone tools (lithics) or for sparking fire.
Geological facts
This specimen displays the typical rounded, weathered exterior common to rocks found in riverbeds or soil. The coordinates (East Java, Indonesia) are rich in volcanic and sedimentary materials where varieties of chalcedony and jasper are abundant.
Field identification & locations
Identify by its hardness (cannot be scratched by a steel knife) and waxy texture. It is a very common find in the southern part of Malang Regency, often associated with ancient volcanic activity and limestone deposits.
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