Heulandite "eyes-chain" from India.

The mineral heulandite is a complex of hydrated calcium-aluminum-tectosilicates with the general chemical formula (Ba, Sr, K, Ca, Na) 2-3Al3 (Al, Si) 2Si13O36 · 12 (H2O). It belongs to the zeolites. The composition of heulandite, that in addition to the elements calcium barium, strontium, potassium and / or sodium may contain, to determine the exact properties. The general properties are; white, yellow, light red, light brown or light gray colors and white stripe color, a glass to pearl luster and perfect cleavage according to the crystal surface [010]. The mean density is between 2.2 and 2.35, and the hardness is 3 to 3.5. The crystal system is monoclinic and the radioactivity of the mineral is hardly measurable. The gamma ray value according to the American Petroleum Institute ranges from 4.3 to 47.06. Heulandite is named after the British mineral collector John Henry Heuland (1778-1856). Like other zeolites, is heulandite for in many different environments: volcanic and metamorphic rocks, pegmatites, tuffiet and deep-sea sediments. The type of location for the calcium variant heulandite is Glasgow in Scotland.