4" Colorless Apophyllite Crystal Cluster on Chalcedony - India

This specimen comes from the Deccan Traps, a large igneous province and one of the largest volcanic features on Earth, in the Pune Province of western India. In the course of quarrying for other materials or digging wells, sometimes large pockets of zeolites and other minerals are unearthed in the volcanic rock.

Apophyllite, while not a zeolite itself, is almost always found associated with zeolites in the same pockets. It has two crystal habits: a rectangular prism capped by a steep four-sided pyramid, or a pseudo-cubic structure. While not a well-known mineral to the general public, it is popular among mineral collectors due to its pastel colors and beautiful crystal formations.

Chalcedony is any microcrystalline variety of silica composed of very fine intergrowths of quartz and mogánite: microcrystalline minerals have microscopic crystals that cannot be observed by the naked eye. Both quartz and mogánite have the same chemical formula SiO2 (silicon dioxide), but different crystal structures. When free from impurities, chalcedony is colorless and transparent. Depending on impurities present during formation, chalcedony can form in a wide variety of colors including red, yellow, green, blue, purple, grey, white, and numerous hues in between. Chalcedony is quite hard at 7 on the Mohs Hardness Scale: this matches its main component quartz, which is the benchmark mineral for the scale at 7.