Zeolite minerals in India are found in amygdaloidal vesicles (called cavities or pockets) in the Deccan lava flows. Zeolites are secondary minerals made up of hydrated aluminum silicate molecules that readily join with cations such as calcium, sodium, or potassium. The word zeolite comes from the Greek zeo (boil) and lithos (stone). The term was first used in 1756 by Axel Fredrik Constedt, a Swedish mineralogist, who found that when heated, stilbite gives off large amounts of water vapor that was locked in the mineral's structure. Today, over 194 aluminum silicate zeolite minerals have been identified.
The Deccan Traps formed 60 to 70 million years ago, during the late Cretaceous period. They were formed by volcanic eruptions, which may have lasted only 30,000 years. They were caused by a deep mantle plume called the Réunion hot spot, that has been connected to the movement of the Indian tectonic plate. Hundreds of volcanic eruptions occurred, flooding an area the size of modern day India with multiple low viscosity flows that varied in thickness from three feet to over 50 feet. As the lava cools, bubble-like fluid and gas vesicles form and merge, and are trapped under the rapidly cooling surface of the flow. As the lava cools and becomes basalt, minerals migrate to and crystallize in these voids, forming the wealth of mineral specimens for which India is justifiably famous.
PROPERTIES & USES
Zeolites have a unique ability to act as "molecular sieves", because zeolites have pores like miniature Swiss cheese that have a unique ability to sort, filter, trap and process a number of materials based on the size of the molecules. They also can act as catalysts, causing chemical reactions to occur. Today, zeolites are used in industry for a wide range of applications, including making laundry detergents, medicine, agriculture, water purification, nuclear reprocessing, and as catalysts.
COLLECTING IN INDIA
Throughout the state of Maharashtra, there are thousands of quarries being worked and wells being dug at any one time. And, there are also thousands of mineral dealers there, all of whom want to get their hands on the best quality specimens available. Because they cannot be everywhere that digging is going on, a "runner" system has evolved as a way for dealers to keep an eye on many of the possible localities for high quality minerals. The runners are local mineral collectors or miners who are paid to bring news of new finds to the bigger dealers, who have groups of runners loyal to them. The competition amongst these groups is often quite intense, as large amounts of money can be at stake, far in excess of what these men can earn at local wage rates.
It is the runners who are usually recognize and preserve India's fine mineral specimens. They show up at the working quarries and well sites whenever there is a blast, so they can pick up, trim and pack the specimens. They work with the miners, pointing out promising zones and telling them about the value of the specimens. Runners usually buy specimens, and then sell them to dealers. For exceptional finds, a group of runners sends one of their friends to the dealer to ask for a cash advance. Most specimens are trimmed by the runners before they are sold. Specimens are often trimmed with a diamond saw, then worked with a hammer and chisel to hide the saw marks. Matrix specimens like large plates and okenite geodes are often sculpted into oval shapes to minimize weight and shipping cost.
THE TOP 10 ZEOLITES
Out of all the 194 naturally occurring zeolites, here are the top 10 favorite zeolites among mineral collectors: Analcime, Barrerite, Chabazite, Heulandite, Mesolite, Mordenite, Natrolite, Scolecite, Stilbite, and Thompsonite. I have included links to the specimens we have available for sale on our web site where possible. I have also thrown in 2 other minerals that are not zeolites (apophyllite and okenite), simply because they are so often found with the other zeolite minerals, and because they are so beautiful and popular. Several of the zeolites shown (barrerite and chabazite) are not from India, because the word's finest examples come from other countries.
1.6" Shiny White ANALCIME Crystal on 2" Matrix - DEK Quarry, Kings Valley OR
Analcime is an interesting mineral. It is sometimes known as analcite, although analcime is preferred. It is one of the few minerals that characteristically forms its own unique crystal - the isometric trapezohedron. The trapezohedron has 24 deltoid-shaped faces, where each face occupies one third of the position of a single octahedron's face.
Analcime, AlSi2O6-H2O is a feldspathoid. Feldspathoids are commonly found in silica-poor igneous rocks, where analcime is sometimes present as well. Nice specimens of anatase are associated with quartz and are considered classics in the mineral world. The good luster, well formed crystal shape and interesting character make analcime a popular mineral for collectors.
3.6" Electric Lime Green APOPHYLLITE Gem Pyramid Crystals with Stilbite-India
Though not a actually zeolite, apophyllite is one of the most common and beautiful minerals that come out of the Deccan Traps. Also, to be mineralogically correct, the Indian variety of this mineral is now called apophyllite-(KF), but to keep it simple, I'll just call it apophyllite.) Apophyllite, whose name roughly means "to leaf apart" in Greek, is a mineral classic. It was given its name because crystals tend to peel or flake apart when they are heated due to the loss of water molecules. Although not that well-known by the general public, apophyllite is quite popular among mineral collectors. It is probably the first exotic mineral that a young collector will own after filling up on specimens of calcite, quartz, pyrite, galena, mica, fluorite, gypsum, apatite, etc. After these common minerals, apophyllite seems like a real rarity and it offers so much to the collector. It has beauty, pastel colors, a bright luster, interesting well formed habits, unusual associations with other exotic minerals and recently large amounts of quality specimens have become available at amazingly low prices from just a decade ago. What more could a collector want in a mineral? What makes apophyllite so popular among collectors is its fantastic crystals with their gemlike vitreous to pearly luster. Apophyllite almost always forms good crystals of two major types. The favorite crystal habit is the rectangular prism capped by a steep four sided pyramid (tetragonal dipyramid). A doubly terminated crystal is exceptionally special. The faces of the pyramids are rotated 45 degrees with respect to the prism faces and so plunge down into the prism edges. This produces a diamond-shaped pyramidal face instead of a typical triangular pyramid face such as on quartz. The shape is an extraordinary example of tetragonal crystal form. Although normally colorless or white, colored examples of apophyllite are always treasured. By far its most impressive color is the pastel green color that augments specimens from Poona, India. Some crystals of apophyllite are cut as gems, but mostly just for collectors. The other common crystal habit is a pseudocubic crystal that occurs when there is no pyramid and the prism is ended by a flat termination (a pinacoid). The pinacoid is a crystal form that is perpendicular to the length of the crystal and so can abruptly terminate the prism. It is often seen as simply truncating the pyramids by cutting off the points of the crystal. When the prism is short and blocky and there are no pyramidal faces, then the pinacoid face can make the crystal appear cube shaped. However the prism faces are commonly striated and all in one direction while the pinacoid is smooth, giving its true symmetry away. Conversely, if the pyramid faces are the only dominant form then the crystal can fool someone in to thinking it is octahedral!
4" White Ivory BARRERITE Lustrous Crystals Kuiu Island Alaska
(Note: Kuiu Island in Alaska produced the finest barrerite specimens in the world)
Barrerite is a tectosilicate mineral. It is an extremely rare zeolite specimen, with the finest specimens coming from Rocky Pass, Kuiu Island, Alaska, USA. It is named for Richard Maling Barrer (1910-1996), a British teacher born in New Zealand who studied zeolites for many years. Barrerite crystal are white to pinkish, with a vitreous-glassy luster and near-perfect cleavage. The crystal system is orthorhombic and is flat and tabular in appearance. It has a Mohs hardness of 3 to 4 and its cleavage is perfect. Barrerite has a white streak and a density of 2.13. It forms on the walls of large fractures in deeply weathered andesitic and rhyolitic lavas.
4.5" Vivid Salmon Orange CHABAZITE Crystals Wassons Bluff Nova Scotia
(Note: chabazite from India cannot compare to fine red-orange chabazites like this one from Nova Scotia)
Chabazite, also known as acadialite, is one of the lesser known zeolites, but still a popular one to collect. Chabazite forms in the petrified bubbles (called vesicles) of volcanic rocks that have had a slight amount metamorphism. Chabazite occurs also in and around hot springs as a precipitate but does not form the wonderful crystals that collectors know from such places as Poona, India. The specimens at Poona are found in the volcanic rock's vesicles with many other zeolites and exotic minerals. One vesicle, which can look like a geode, can have an amazing assortment of minerals and chabazite is sometimes a key component in these veritable mineral treasure troves. The mix may contain sprays of natrolite's or scolecite's bright, needle thin crystals, curved pink crystals of stilbite and blocky, pearly, coffin shaped crystals of huelandite. Included in this diverse mix and making its own marked distinction in character could be the angular, vitreous, pseudocubic crystals of chabazite. The typical crystal of chabazite is a rhombohedron. A rhombohedron is basically a "squashed" cube. However, in chabazite the rhombohedrons are not "squashed" that severely and the angles between the crystal faces are nearly 90 degrees. Consequently, chabazite crystals will often look cubic or pseudocubic (pseudo = false). Chabazite's structure has a typical zeolite openness that allows large ions and molecules to reside and actually move around inside the overall framework. The structure actually contains open channels that allow water and large ions to travel into and out of the crystal structure. The size of these channels controls the size of the molecules or ions and therefore a zeolite like chabazite can act as a chemical sieve, allowing some ions to pass through while blocking others.
4.7" Vivid Teal Blue Green HEULANDITE Sharp Shiny Curved Crystals - India
Heulandite is one of the most common and one of the most well known members of the Zeolite Group. It can have a nice pearly luster and lovely colored hues. It forms wonderfully complex and quite unique crystals and is often associated with other rare and beautiful minerals. Rarely are the larger crystals transparent, but they always have a certain depth of translucency. Heulandite forms large crystals in the vesicles of volcanic rocks that have had a slight amount of metamorphism. Huelandite occurs in other environments but does not generally form large well shaped crystals in those situations. Heulandite gets its name in honor of John Henry Heuland, a British mineral collector and dealer. Heulandite is the name of a series of tectosilicate minerals of the zeolite group. It was first discovered in 1818. Prior to 1997, heulandite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a series of names, including Heulandite-Ca, which is the most common. Heulandite forms monoclinic rhombic crystals, typically coffin-shaped. They can also appear to be wedge shaped, if only the ends of the crystals are visible. Heulandite is typically clear to white, or may be yellow, brown, orange or even red. It appears green when celadonite crystals are included. It has a hardness of 3-4, and a specific gravity of 2.2.
4.3" White MESOLITE BALL-Long Radiating Needle Crystals - India
Mesolite is a popular zeolite mineral for mineral collectors and zeolite collectors in particular. Its radiating sprays of ice-clear acicular crystals are a hallmark of this mineral. Often associated with minerals such as green or clear apophyllite, pink and pearly heulandite and sparkling tiny crystals of quartz, mesolite is wonderful both alone and in mineral assemblages. Mesolite crystals are made of chains of silicate tetrahedrons aligned in one direction, forming sprays and balls of long, needle-like crystals. It has a specific gravity of 2.3, and a hardness of 5.5.
4.9" White MORDENITE Radiating Crystal Balls to 2" on Stilbite - India
Mordenite is one of the rarer, but still somewhat more widespread, members of the zeolite group of minerals. Mordenite belongs to this last category. It was discovered in 1864 by Henry How, who name it for the town of Morden, Nova Scotia, Canada, on Bay of Fundy, where it was first found. Mordenite forms fine sprays of radial acicular crystal clusters that look like pincushions or snowballs. On top of other interesting and beautiful associated minerals, mordenite can be extremely striking. Mordenite is definitely a must have especially for the dedicated zeolite collector. Mordenite crystals are orthorhombic, forming fibrous balls and masses, and occasionally long, hairlike crystals. It is clear, white, or faintly yellow or pink, and has a hardness of 5 and a density of 2.1.
9.1" Peachy Pink NATROLITE Intricate Radiating Needle Crystals - Argentina
Natrolite is a common and popular zeolite mineral. Its radiating sprays of ice clear acicular crystals are not exclusive to natrolite but they are a hallmark of this mineral. Natrolite can make a fine specimen in itself but it often is an accessory to other minerals and can enhance the beauty of associated minerals such as apophyllite, heulandite, benitoite and others. Natrolite's structure has a typical zeolite openness about it that allows large ions and molecules to reside and actually move around inside the overall framework. The structure contains open channels that allow water and large ions to travel into and out of the crystal structure. The size of these channels controls the size of the molecules or ions, and therefore zeolites like natrolite can act as a chemical sieve. Natrolite's structure contains chains of silicate tetrahedrons aligned in one direction; this produces the needle-like crystals. Its cleavage results from the weaker bonds between the chains. Natrolite derives its name from natron, the Greek word for soda, and lithos, meaning stone. It has a specific gravity of 2.2 and a hardness of 5.5.
4.4" White Puffy OKENITE Crystal Balls Tucked Inside a Basalt Geode India
Though not a zeolite, okenite is a silicate mineral that is usually associated with zeolites, and is one of the most popular mineral species found in the Deccan Traps. It is most commonly found as small white "cotton ball" formations within basalt geodes. These formations are clusters of straight, radiating, fibrous crystals that are both bendable and fragile. It was named for the German naturalist, Lorenz Oken (1779-1851, from the type locality on Disko Island, Greenland. Okenite is an unusual mineral. It frequently forms radiating clusters where the crystals are so thin they look like tiny fibers. The clusters are composed of straight, radiating, thread thin, crystals. These clusters can make for very attractive specimens and often accompany many fine and rare minerals such as apophyllite, gyrolite and many of the zeolites. Volcanic vesicles that enclose these delicate tufts of okenite create a mesmerizing crystal wonderland landscape, and are called "okenite geodes".
5.6" Snow White SCOLECITE Snowball with Sharp Undamaged Crystals - India
Though somewhat rare, scolecite is a popular mineral among collectors. It forms in volcanic bubbles called vesicles along with other zeolites. Scolecite's sprays of radiating crystals are exotic, inspiring, awesome, and magnificent. They are truly hard to describe, but are something that everyone who loves minerals will enjoy. Scolecite's structure has a typical zeolite openness about it that allows large ions and molecules to reside and actually move around inside the overall framework. The structure contains open channels that allow water and large ions to travel into and out of the crystal structure. The size of these channels controls the size of the molecules or ions and therefore a zeolite like scolecite can act as a chemical sieve. Scolecite's structure contains aligned chains of silicate tetrahedrons. This produces the needle-like crystals and the cleavage results from the weaker bonds between the chains. Scolecite, a calcium zeolite, natrolite, a sodium zeolite, and mesolite, a calcium and sodium zeolite, are closely related and sometimes found together. The presence of calcium in two of the minerals slightly alters the structure from that of natrolite; from an orthorhombic symmetry to a monoclinic symmetry. However, twinning of scolecite and mesolite often make them look orthorhombic All three minerals are referred to as "chain" or "needle" zeolites. They are similar and hard to distinguish when in clusters with radiating, acicular habits. Natrolite tends to forms thin crystals with pyramidal terminations, but mesolite's fibrous crystals are usually the thinnest crystals of the three minerals. Scolecite's larger crystals tend to be more robust and durable. These characteristics are only generalities and can not be used as dependable identifying traits. Absolute identification can not be made by ordinary means.
3.8" Red-Orange STILBITE Crystal Bow Tie - India
Stilbite commonly forms nice crystals inside the petrified bubbles (called vesicles) of volcanic rocks that have undergone a small amount of metamorphism. Stilbite is a common and perhaps the most popular zeolite mineral for collectors. Stilbite crystals can aggregate together to form a structure resembling wheat sheaves This hourglass structure looks like several crystals stacked parallel to each other with the tops and bottoms of this structure fanning out while the middle remains thin. Stilbite's hallmark crystal habit is unique to stilbite and a rarer but related zeolite called stellerite. Whether in the wheat sheaves or not, stilbite can be a handsome specimen with its pearly luster and often colorful pink tints. Stilbite commonly forms nice crystals inside the petrified bubbles (called vesicles) of volcanic rocks that have undergone a small amount of metamorphism. Stilbite's structure has a typical zeolite openness about it that allows large ions and molecules to reside and actually move around inside the overall framework. The structure contains open channels that allow water and large ions to travel into and out of the crystal structure. The size of these channels controls the size of the molecules or ions and therefore a zeolite like stilbite can act as a chemical sieve. Stilbite's structure contains rings of aluminosilicate tetrahedrons oriented in one direction and this produces the prominent pinacoid faces, the perfect cleavage and the unique luster on those faces.
3.3" Very Rare Zeolite THOMSONITE Velvety Crystal Balls '05 - India
Thomsonite is one of the rarest zeolites. It forms tight acicular radiating clusters and sphericules as well as some blockier crystals that are found in the vesicles or bubbles of volcanic rock as are most other zeolites. The color is usually colorless or white, but some highly prized specimens are brick red, and a few have shown a lovely yellow color. Thomsonite is a rare mineral and is highly sought after by collectors of rare zeolite minerals. Now reclassified as thomsonite-Ca or thomsonite-Sr. Thomsonite was first found in Scotland in 1820, and was named after Thomas Thomson, the Scottish chemist. Thomsonite belongs to the orthorhombic crystal system. It has a hardness of 5 to 5.5, and is transparent to translucent with a density of 2.3 to 2.4. The elongated, bladed crystals typically form tight hemispherical acicular radiating clusters and sphericules, fans and tufts. The aggregates can look spiky, ball-like, or can even form worm-like growths.