3.65" Peach Heulandite and Apophyllite on Chalcedony - India

Heulandite is a mineral of the zeolite group that also fits within the silicate and tectosilicates groups. It has the general chemical formula (Ca,Na)2-3Al3(Al,Si)2Si13O36 · 12H2O, but the calcium and sodium can be substituted by potassium, barium, or strontium ions. Heulandite crystals will often form as distinctive tabular, radiating crystals with a vitreous luster, and can display a variety of colors including white, green, brown, orange, red, pink, yellow, grey, and black.

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.