A large family of minerals known as zeolites tends to form in the bubbles in lava after it has frozen, particularly in the vesicles in low silica basalt. As the lava cools from the outside in, any water it contacts tends to heat up and leach elements, carrying them upwards through the rock stack in a giant convection cell. Higher up some of these leached elements are precipitated as the hot mineralised fluids encounter a change in chemical or pressure/temperature conditions great enough to destabilise the solution and force minerals to precipitate out. Needless to say they tend to do so in the available pore space, usually ex bubbles in the lava. It is also found in sinters around volcanic hot springs, brought to the surface by similar fluids.
Chabazite is a whole zeolite family of its own, with calcium, potassium, sodium and strontium rich versions all dependent on the precise chemistry of the fluid whose contents were deposited. The resulting colours vary from colourless and white to orange, brown, pink, green, reddish or yellow, sometimes with colour zoning. The Mohs hardness also varies with chemistry, from 3-5 on the scale. Like the rest of the zeolite family it is therefore too soft for jewellery use.
It was named in 1788 by Louis-Augustin Bosc d'Antic after the Greek word for melody taken from one of the Orphic mystical poems from antiquity that discusses minerals, though it also goes under the name of Acadialite, after the part of Canada where it was discovered. It is also found in the Deccan trapps of India (especially around Poona), amongst Iceland's basalts, the Faroe Islands (amongst other parts of the great North Atlantic Igneous Province that erupted as America split off from Europe), Giant's Causeway in Ireland and the Columbia flood basalts of the western USA. It often occurs in association with other zeolites in a single geode.
Here we have several orangey yellow rhombs with a near cubic form on matrix from Nova Scotia in Canada, measuring 8.5 x 6.6 x 4.3 cm
Image credit: Rob Lavinsky/iRocks.com
http://www.minerals.net/mineral/chabazite.aspx https://www.mindat.org/min-956.html http://www.galleries.com/Chabazite
