sedimentary
Green Chert (Jasper)
Microcrystalline Quartz (SiO2) with chlorite/epidote inclusions
Hardness: 6.5-7 (Mohs); Color: Sea-foam green to olive with reddish-brown iron staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Sea-foam green to olive with reddish-brown iron staining
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Sea-foam green to olive with reddish-brown iron staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed from the accumulation of silica-rich organic remains or chemical precipitation in marine environments. The green hue often results from silicate minerals like chlorite. The East Java region (8.4 S, 112.7 E) is rich in volcanic and sedimentary sequences where such silicates are common.
Uses & applications
Historically used for stone tools; currently used as lapidary material for cabochons, decorative stones, and in landscaping.
Geological facts
Green chert is often locally called 'green jasper' in Indonesia. This specimen shows classic conchoidal (shell-like) fracturing and significant oxidation (iron rust) on its exterior surfaces.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and smooth, curved fracture surfaces. Common in riverbeds and volcanic deposits in East Java.
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