gems, quartz, agate, chalcedony, jasper, onyx, flint, chert

Cryptocrystalline varieties of quartz—including chalcedony, agate, jasper, onyx, flint, and chert—appear amorphous in hand specimens but display double refraction under the microscope, indicating their hidden crystalline structure. These varieties are found in several Indian states, including Gujarat, Uttar Pradesh, Tamil Nadu, Andhra Pradesh, Maharashtra, Madhya Pradesh, Karnataka, and Punjab. The most significant agate deposits occur in Gujarat, particularly in the Ratnapur and Rajpipla areas, and westward between the Tapi and Narmada rivers in Bharuch district, where agate is found as river-washed pebbles of various sizes. Other economically important sources include districts in Maharashtra (Amravati, Aurangabad, Buldhana, Chandrapur, Nashik, and Pune), Andhra Pradesh (beds of the Krishna and Godavari rivers), Jharkhand (Dumka), Madhya Pradesh (Dhar, Mandsaur, Sihore, and Shahdol), and Gujarat’s Kachchh district.