What are minerals?
Before we can explain what a zeolite is, it’s crucial to understand minerals more generally. Minerals are inorganic, naturally-occurring chemical compounds or elements that form with an orderly internal structure. For example, salt and sugar are both crystalline, but sugar is not considered a mineral because it’s artificially created, whereas salt occurs naturally (generally speaking). Most minerals result from drying liquid magma, or primary or secondary hydrothermal solutions. Their ultimate formation depends highly on the environment — which elements and compounds are present, the temperature, and the pressure.
What are zeolites?
Zeolites, then, are crystalline minerals made from silicon, aluminum, and oxygen, along with alkaline-Earth metals like magnesium, sodium, and potassium. What really makes them special and what gives them their name is that water gets inside them. Axel Crondstedt, known for discovering nickel, coined the term zeolite, which means “boiling stones” in Greek. When heated, you can actually see zeolites bubble — but the minerals themselves don’t burn, and won’t melt until temps hit 1,000 degrees Celsius! Another fun fact: zeolites actually give off heat when rehydrated. They’re truly fascinating minerals.
Why Indian zeolites?
Zeolites are found all over the world, with most of them coming from China, but each location produces completely unique varieties of zeolites. Indian zeolites come from an area of Maharashtra, India called the Deccan Traps, a massive area of ancient lava flows over 6,500 feet thick over 200,000 square miles. The reason we find geodes and pockets of all kinds is that as the lava cooled, bubbles of gas collected in certain areas along with minerals, which provided the recipe for India’s fantastic mineral wealth. As India grows, zeolites are often destroyed in the process for mining basalt, which is used to pave roads. That makes each zeolite extremely special, and part of a special economy in their respective localities.
Apophyllite is generally found as a secondary mineral in vesicles in basalts and other volcanic rocks. They're fairly prevalent around the world, though Indian apophyllites are famous for their termination points and also cubic forms. It comes in green, red, white, gray green, brown, pink, purple, and orange. With its various colors and relative affordability, apophyllite is a must-have for any collector, and often the first in a collection. Its name comes from Greek, meaning "flakes apart like a leaf," describing the effect when it becomes dehydrated.
Calcite: Ca CO3
Calcite is easy to get confused, as it's one of the most common minerals and it forms in a huge variety of colors, shapes, and textures. The calcite from India, you'll notice, are generally yellow and cubic or brown "dogtooth" type crystals. Calcite is a polymorph of aragonite, meaning they have the same chemical composition but a different chemical structure, and this difference generally requires an optical test to see. Calcite is a German word, derived from the Latin term for lime, calx.
Stilbite is one of the most abundant crystals found in the Deccan Traps, forming with almost every zeolite found there. It's famous for tabular shapes called “blades,” and thicker “bow tie” formations, which are quite unique. It's found in white, pink, peach, yellow, orange, brown, beige, gray, red, and green. Stilbite gets its name from Greek, meaning "to glitter," as stilbite can be quite lustrous.
Amethyst is identified as its own mineral, but it's really a violet or purple variety of quartz sought after for its brilliant colors. The purple is the result of minor Iron inclusions and gamma radiation during formation. And although the color can be quite intense, don't leave amethyst in the sun, as the color fades with UV radiation. Just like quartz more generally, amethyst comes in a variety of forms, like scepters, split growths, single crystals, and even druzy aggregates. Its name comes from Greek, “not drunk,” for the belief that it could sober folks up.
Cavansite is known for its brilliant blue-green color, though it comes in rarer shades of blue prized by collectors. It has a vitreous luster and a rather globular form, with a feathery texture. It's known to be found in Oregon, but more commonly, this mineral comes from the Pine district of Maharashtra, India. It's a brittle crystal, moreso than many of the zeolites and associated minerals. One of the most fun facts about cavansite is its name — it's named for the chemical structure of Ca(VO)Si4O10•4(H2O (Calcium Vanadium Silicate).
Chalcedony is just a fancy term for microcrystalline quartz, though its tiny size and formation make it quite distinct. Chalcedony can form coral-like stalactites full of other minerals, and cover the matrix of geodes, in a variety of colors, mostly white, black, grey, and blue-grey. It can also form in globular forms, like botryoidal stalagmites.
Fluorite: Ca F2
Fluorite is one of the more popular minerals, coming in all colors of the rainbow in a variety of shapes. As the name suggests, it's famous for fluorescent reactivity, adding even more color variation for collectors who play with lighting. The fluorites you'll see from India are botryoidal (rounded and globular), and yellow or red, which is sought after for its rarity. When discovered in 1797, it was named from Latin, fluere, meaning "to flow." And the term fluorescence — and the name for the element Fluorine — is actually derived from fluorite, rather than the other way around.
Goosecreekite has a funny name, but its rarity and relatively recent discovery make it quite special. This coveted zeolite was recognized as a distinct mineral in 1980, named for the Goose Creek Quarry in Leesburg, VA. Despite its place of discovery, this white or transparent globular zeolite is more often found in India than the US, specifically in Jalgaon and surrounding localities. It's commonly found with other zeolites, like prehnite, calcite, heulandite, and stilbite.
Gyrolite: Na Ca16(*Si23Al) O60 (OH)315H2O
Though gyrolite is not a zeolite, it occurs with zeolites like apophyllite, natrolite, and other associated minerals like okenite, prehnite, and calcite. It appears yellow, brown, white, or light green, and is no harder than a fingernail (2.5 hardness). It's also fluorescent. Its rounded form of groupings earned it the Greek name for circle, or "guros." Gyrolite is quite rare, but it can certainly be found.
Heulandite: (Na Ca)2 Al3 (Al,Si)Si13O36 12H2O
Heulandite is another very common zeolite. It's known for its coffin-like shape and tabular crystals. Due to its sometimes similar colors, it can be confused with stilbite, especially smaller crystals making up a matrix. It comes in white, clear, red, yellow, brown, and green. Its name comes from Henry Heuland, an English mineral dealer who collected zeolites from Iceland.
MM Quartz: SiO2
Quartz is everywhere, one of the most commonly known minerals and an extremely common mineral generally. Because of its wide distribution, knowledge of quartz is prehistoric, with the earliest name coming from Theophrastus, 300-325 BCE. The first recorded use of today’s term comes from 1500s German physician Ulrich Rulein von Kalbe. Its pure form is transparent and colorless, lustrous and terminated. Though it is not a zeolite various forms of quartz often form with zeolites, especially amethyst and chalcedony.
Okenite: Ca10Si18O46 18H2O
Okenite was originally discovered in Greenland, but it occurs in other localities, including Bombay and Pune in India, forming commonly with zeolite minerals. It forms as what looks like spiky cotton balls, with tiny sharp terminations. It's an extremely brittle mineral, though it's a 5 in hardness. Sometimes it forms with gyrolite, combining two quite rare minerals. Named after the 18th Century German biologist Lorenz Oken.