Chert (Quartz var.)

Hardness: 7 (Mohs scale), Color: Beige, tan, or reddish-brown with white bands/vessels, Luster: Waxy to vitreous, Crystal Structure: Cryptocrystalline quartz, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by the replacement of limestone with silica via groundwater. Common in sedimentary basins and often found as nodules or layers.

Historically used for stone tools (flintknapping); currently used as a raw material for ceramics, construction aggregate, and as a semi-precious lapidary material for jewelry and cabochons.

Chert is so hard that it can strike sparks from steel. The user's note about it being difficult for a diamond blade suggests a very high silica content. The 'little diamonds' described are likely druzy quartz crystals that grew in small cavities or fractures within the specimen.

Identify by its extreme hardness (cannot be scratched by a steel knife) and waxy texture. Found frequently in the Trans-Mexican Volcanic Belt region where silica-rich geological activity is common. Small druzy quartz crystals inside are a common diagnostic feature.