Zeolites, a really special mineral group

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I always was interested in minerals which are not only aesthetic but also have a use in our day to day life. The zeolite group of minerals fits both descriptions (at least in my opinion).

Zeolite - synthetic word formed from "zein" (greef for to boil) and "lithos" (greek for stone/rock) points towards one of the defining physical properties of the mineral group: All zeolites contain amounts of water bound in their crystal grid, which will evaporate (and thereby make the rock seemingly boil) when heated. Nowadays the technical use of Zeolites is limited mainly to synthetic Zeolites, which are for example used as molecular sieves (amongst a whole bundle of other uses; there is a lot of scientific research going on into the properties of the known Zeolite types, as well as research into new kinds of zeolites).

My main interest in Zeolites is the wide range of beautiful (and affordable) crystals that they form. Over the next few months I will try to present a range of pictures here that show these crystals in their full beauty.


At the time I wrote this, these are the minerals belonging to the group of zeolites (if you ignore the latest change by the IMA in the zeolite nomenclature, which didn't in the least help the casual collector):
Amicite K2Na2Al4Si4O16 · 5 H2O
Amicite on Natrolite and Ägirine, Mt. Kukisvumchorr, Kola Peninsula, Russia. The best Amicite crystal is seen exactly in the middle of the picutre and is about 1mm in size.
Analcime NaAlSi2O6 · H2O
Analcime, Talisker Bay, Isle of Skye, Scotland.
Analcime, Talisker Bay, Isle of Skye, Scotland.
Barrerite (Na,K,Ca)2Al2Si7O18 · 7 H2O
Bellbergite K,Sr,Ba)2Sr2Ca2(Ca,Na)4Al18Si18O72 · 30 H2O
Bikitaite LiAlSi2O6 · H2O
Boggsite (Ca,Na)11(Si,Al)96O192 · 70 H2O
Brewsterite (Sr,Ba,Ca)Al2Si6O16 · 5 H2O
Chabazite CaAl2Si4O12 · 6 H2O
Chabazite, Quiraing, Isle of Skye, Scotland.
Chabazite, Talisker Bay, Isle of Skye, Scotland.
Cowlesite CaAl2Si3O10 · 5-6 H2O
Dachiardite (Na,K,Ca0.25)5Al5Si19O482 · 14 H2O
Edingtonite BaAl2Si3O10 · 4 H2O
Epistilbite CaAl2Si6O16 · 5 H2O
Epistilbite, Lonavla, India.
Erionite (K2,Ca,Na2)2Al4Si14O36 · 15 H2O
Faujasite (Na2,Ca)Al2Si4O12 · 8 H2O
Ferrierite (Na,K)2Mg(Si,Al)18O36(OH) · 9 H2O
Garronite Na2Ca5Al12Si20O64 · 27 H2O
Gismondine Ca2Al4Si4O16 · 9 H2O
Gmelinite (Na2,Ca)Al2Si4O12 · 6 H2O
Gmelinite with Chabazite, Sokolov-Sarbay mine, north Kazakstan.
Gobbinsite Na4(Ca,K2,Mg)Al6Si10O32 · 12 H2O
Gonnardite Na2CaAl4Si6O20 · 7 H2O
Goosecreekite CaAl2Si6O16 · 5 H2O
Gottardiite Na3Mg3Ca5Al19Si117O272 · 93 H2O
Harmotome (Ba,K)1-2(Si,Al)8O16 · 6 H2O
Harmotome on Calcite, Whitesmith Groove, Strontian, Scotland. As is common with this mineral all of the crystals are twinned. Strontian in the scottish highlands is the type locality for Strontianite, Harmotome and Brewsterite.
Herschelite (Na,Ca,K)AlSi2O6 · 3 H2O
Heulandite (Na,Ca)2-3Al3(Al,Si)2Si13O36 · 12 H2O
Heulandite, road cut near Edinbane, Isle of Skye, Scotland.
Klinoptilolite (Na,K,Ca)2-3Al3(Al,Si)2Si13O36 · 12 H2O
Laumontite CaAl2Si4O12 · 4 H2O
Laumontite on Analcime, road cut between Salen and Tobermory, Isle of Mull, Scotland. Unfortunately the dehydration of the crystals already begun - as is usual for this Zeolite. In the end this will destroy the crystal grid and the Laumontite will break up completely. There are several methods to prevent this decay but they didn't work to my satisfaction... For some specimen this is a real threat, since the other Zeolites were depositied after the laumontite and if they didn't form a continuous layer these specimen are usually doomed.
Levyne (Ca,Na2,K2)Al2Si4O12 · 6 H2O
Levyne crystals of up to 3mm with unknown Zeolite (probably Thomsonite), Finagles Pinnacles, Isle of Skye, Scotland.
Levyne crystals of up to 3mm with unknown Zeolite (probably Thomsonite), Finagles Pinnacles, Isle of Skye, Scotland. This is an alternative view of the previous specimen.
Levyne crystals of up to 2mm, Finagles Pinnacles, Isle of Skye, Scotland.
Maricopaite Pb7Ca2Al12Si36O100 · 32 H2O
Mazzite K2CaMg2(Al,Si)36O72 · 28 H2O
Merlinoit (K,Ca,Na,Ba)7Si23Al9O64 · 23 H2O
Mesolite Na2Ca2Al6Si9O30 · 8 H2O
Mesolite on Analcime, Talisker Bay, Isle of Skye, Scotland.
Montesommaite (K,Na)9Al9Si23O64 · 10 H2O
Mordenite (Ca,Na2,K2)Al2Si10O24 · 7 H2O
Mordenite on Quartz, Kolgaon, India. Size of the Mordenite-balls approx. 1-1.5 cm (~0.5 inch)
Natriumdachiardite (Na2,Ca,K2)4-5Al8Si40O96 · 26 H2O
Natrolite Na2Al2Si3O10 · 2 H2O
Natrolite, Malad quarry near Bombay, India.
Offretite (K2,Ca)5Al10Si26O72 · 30 H2O
Paranatrolite Na2Al2Si3O10 · 3 H2O
Paulingite (K,Na)2Ca(Si13Al4)O34 · 13 H2O (?)
Perlialite K9Na(Ca,Sr)Al12Si24O72 · 15 H2O
Phillipsite (K,Na,Ca)1-2(Si,Al)8O16 · 6 H2O
Pollucite (Cs,Na)2Al2Si4O12 · 0.5-1 H2O
Scolecite CaAl2Si3O10 · 3 H2O
Stellerite CaAl2Si7O18 · 7 H2O
Stellerite, road cut near Edinbane, Isle of Skye, Scotland. This relatively rare Zeolite is quite abundant in an amygdale lava layer here. It is accompanied by Calcite, Stilbite and Heulandite. The association with Stilbite which is closely related to Stellerite makes it quite hard to distinguish both minerals. The specimen shown hasn't been tested but the crystal habit and the Calcite present in the other half of the amygdale suggest it really is Stellerite.
Stellerit, Malad quarry near Bombay, India.
Stellerit, Rudny, Kazachstan.
Stilbite NaCa2Al5Si13O36 · 14 H2O
Stilbite, Aurangabad, India. This Stilbite is exceptionally colored, normal colors would be cremewhite and rose.
Tetranatrolite Na2Al2Si3O10 · 2 H2O
Terranovaite NaCaAl3Si17O40 · 7-13 H2O
Thomsonite NaCa2Al5Si5O20 · 6 H2O
Thomsonite on Chabazite, The Quiraing, Isle of Skye, Scotland. The size of the Thomsonite aggregates on this specimen is only 2 mm but the contrast of the white Thomsonite to the seemingly reddish Chabazite (the rock is colored rather red so this color is transmitted through the very clear Chabazites) makes this a very attractive specimen for both minerals.
Thomsonite, Hammer-Unterwiesenthal, Germany.
Tschernichite (Ca,Na)(Si6Al2)O16 · 4-8 H2O
Wairakite CaAl2Si4O12 · 2 H2O
Wellsite (Ba,Ca,K2)Al2Si6O16 · 6 H2O
Willhendersonite KCaAl3Si3O12 · 5 H2O
Yugawaralite CaAl2Si6O16 · 4 H2O
Yugawaralite, Malad quarry near Bombay, India. Size of the Yugawaralite cristal on the left hand side of the amygdale approx. 1.5 cm (~0.7 inch).


The Zeolites are naturally not the only minerals forming interesting crystals. Many times the associated minerals are as interesting as the Zeolites themselves. Here is a non representative selection of associated species:

Apophyllite KCa4Si8O20(F,OF) · 8 H2O
green Apophyllite on Stilbite, Pune, India. Size of the largest crystal 2.0 cm. Although Apophyllite is represented on many specimen you mustn't make the mistake of thinking of Apopyllite as a Zeolite. Apophyllite itself is a small group of minerals (consisting of Fluorapophyllite, Hydroxylapophyllite and Natroapophyllite) which can only be distinguished by detailed analysis, so all of them are labeled the same when they end up on the mineral market. The same fate lies ahead for many of the Zeolite species, as the IMA has just changed the nomenclature to be more precise (well really taking the chemistry a bit more serious, and thereby loosing the simplicity for the collectors at determining species).
Cavansite Ca(V4+O)Si4O10 · 4 H2O
Cavansite on Heulandite, Wagholi quarry near Pune, India. Size of the Cavansite ball in the middle of the picutre approx. 2.0 cm. This locality is co type locality of Cavansite and is currently the world's best locality for this minerals (on quality as well as on quantity).
Cavansite on Heulandite, Wagholi quarry near Pune, India. Size of the Cavansite ball in the middle of the picutre approx. 2.0 cm. This locality is co type locality of Cavansite and is currently the world's best locality for this minerals (on quality as well as on quantity).
Powellite CaMoO4
Powellite on Stilbite, Pandulena mountains near Nasik, India. Size of the biggest Powellite 1.5 cm. On this picture you should be able to make out at least four of the 11 Powellite crystals on this gorgeous specimen.
Calcite CaCO3
Calcite on Chabasite and Thomsonite, The Quiraing, Isle of Skey, Scotland. Size of the biggest Calcite is 2 cm.
Gyrolite NaCa16(Si23Al)O60(OH)5 · 15 H2O
Gyrolite with Calcite on Quartz, Malad quarry near Bombay, India.
Pectolite NaCa2Si3O8(OH)
Pectolite, Silbach quarry, Germany. Usually the Pectolite forms massive veins that show interesting fibrous structures. In this rare example there was room enough in the vug for the Pectolite to form free standing crystals. At some locations the Pectolite is an early component in Zeolite bearing rocks and the Zeolites form on a layer of Pectolite.
Okenite Ca10Si18O46 · 18 H2O
Okenite with Apophyllite on Laumontite, Malad quarry near Bombay, India. Unfortunately this locality is closed now and Okenite of this Quality is not known from any other locality yet. One can only hope that this will change with the continued development of the quarries in India and elsewhere. Typical minerals associated with Okenite are Laumontite, Gyrolite, Apophyllite, Calcite and Prehnite, which can all appear on one specimen.


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All Pictures are © 1999 by Karl Günter Wünsch - Email: kgw@mineralien-verkauf.de