8.6" Heulandite, Apophyllite and Stilbite on Mordenite - Composite

This specimen comes from the Deccan Traps, a large igneous province and one of the largest volcanic features on Earth, near the city of Pune in western India. As miners quarry for other materials or dig wells, they sometimes unearth large pockets of zeolites and other minerals in the volcanic rock.

Stilbite is probably the most common zeolite found in these deposits. Crystals often form flowery, bowtie. or hourglass-shaped structures and come in a variety of colors. Some of the most beautiful colorations are the pink or peach tints. While not a zeolite itself, apophyllite 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.

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.