The Zeolites: A Family of Useful Minerals

The term zeolite denotes a family of minerals with similar chemical structures. They are all aluminum- silicate minerals that have crystal structures which resemble honeycomb. Zeolite minerals are often found in vesicles inside volcanic rocks, especially basalt. There are about fifty minerals in the zeolite group.
The honeycomb-like structure found within the zeolites includes a lot of tiny tunnels and pores that allow water to pass through the mineral without affecting its crystal; and these pores are all of a uniform size. Now ask yourself: does it seem that something like this could occur by chance or do you think it points to the design of a Creator? It’s something worth thinking upon.
Because of the properties that I mentioned above, zeolite minerals are often used to filter very small particles out of air and water. They can also hold water like sponges so they are used thus and in place of potting-soil in some agricultural applications. Zeolites are used to clean up oil spills and radioactive waste as well.
Zeolite minerlas are found in many different countries far too numerous to mention here. I plan to write about some of the members in this family of useful minerals soon and their properties and locations can be discussed on an individual basis.

Antimony's Toxic Legacy

When I made my last post I said that I planned to talk about the metal antimony’s toxic legacy. I researched the topic and found nothing concerning the symptoms of antimony poisoning save that antimony compounds attack certain tissues in the body. I have read that consuming large enough doses of antimony or its compounds is lethal. In fact, antimony’s very name is said to come from a story in which a monk named Valentinus added stibnite to the other monks’ food in an attempt to help them gain weight. Unfortunately the stibnite did not have its desired effect and the monks died. After that it was called anti-monachium which means “against monks.”
So where does this leave our shiny, gray mineral stibnite? Well if you were to eat a large enough quantity of stibnite you would die, but handling the mineral isn’t the same as consuming it. I have always read that you should wash your hands carefully after handling stibnite. Don’t let young children touch it--keep it out of their reach. I keep mine in a plastic “perky box” to minimize contact with it.
Stibnite is a beautiful mineral, one that I am happy to include in my collection. It should not be feared, but rather respected. Follow the safety rules that I have mentioned above and use common sense when collecting stibnite.

Stibnite: Toxic Beauty

The metal antimony was once called stibium, which is why it is represented by an Sb on the Periodic Table of Elements. Stibnite’s name stems from the fact that it is an ore of antimony.
Stibnite is a steel-gray or lead-gray mineral that has a metallic luster (although it can tarnish, turning black) Stibnite’s crystals are orthorhombic and are usually blade or needle-shaped. Its crystals are slightly flexible so they can be bent or twisted. I wouldn’t do this with any good specimen, but it could be a helpful test to help identify the mineral. Stibnite measures only a 2 on the Mohs scale of hardness.
Stibnite is still the main ore of antimony, which has been used since ancient times (though for many years it was confused with lead) Today antimony is mixed with other metals to form alloys that are used as coverings for cables and in car batteries. Stibnite itself is used in the making of matches, percussion caps, and fireworks.
Stibnite is found in places like: Japan, Serbia, Macedonia, Romania, Peru, California, and Nevada.
A final word of caution: stibnite is a poisonous mineral! Antimony is toxic and it imparts this property to its ore. Always wash your hands carefully after handling stibnite. This topic will be discussed further in my next post.

Anhydrite: Warning! Keep Dry!

The word “anhydrous” means “lacking water.” So, when gypsum looses the water molecules that help make up its chemical composition “anhydrite” is an apt name for the new mineral that results.

Anhydrite commonly forms when gypsum dehydrates, but it can form in other ways. It is often found between layers of gypsum and even between gypsum and halite. Because it usually forms when gypsum dries out the layers of anhydrite are often contorted.

Anhydrite crystallizes in the orthorhombic crystal system, but it is usually found in massive or fibrous habits, the latter looking a bit like satin-spar selenite (a variety of gypsum that you can read about in my March 17, 2011post Gypsum: The Mineral About the House) Anhydrite can be distinguished from gypsum by the fact that it is a little harder. Anhydrite is usually white or colorless, but it can also be lavender, reddish, bluish, or gray.

I’ve already stated that gypsum becomes anhydrite when it looses its water, but if the anhydrite absorbs water then it will become gypsum once again. Because of this, anhydrite can be ground into a powder and used to make concrete and plaster of Paris. This property also makes anhydrite difficult to find. Since it so easily reverts to gypsum, anhydrite tends only to be found deep underground where it won’t be exposed to much moisture.

Anhydrite can be found in such places as: Mexico, Cuba, Peru, Chile, Canada, Zaire, and the American states of: Alabama, Michigan, Louisiana, and Texas.

I hope that you’ve enjoyed this piece about anhydrite. I have one final note for collectors which concerns anhydrite’s relationship with gypsum: if you want to collect the stuff it is a good idea to keep it in an airtight case with some silica gel. Otherwise your anhydrite specimen might revert to gypsum!

Flint: Sedimentary Quartz

Flint is a variety of a sedimentary rock called chert. Chert is composed primarily of micro-crystalline quartz and can be many colors, but when it contains a lot of fossilized algae it becomes black and is called “flint.” Technically any chert that is black or toffee-colored is called “flint.”
Flint is formed when calcite in limestone is replaced by silica, thus flint is often found with limestone or even contained within a limestone shell (This can be seen in the first picture) In Kentucky’s Mammoth Cave large nodules of the stuff are found poking out of the cave’s limestone walls! Flint has a glassy texture and breaks with a conchoidal fracture like obsidian. Flint is amorphous, meaning that it has no distinct shape, but it is often found as lumps. Many years ago flint filled the Y and T-shaped tunnels of ancient creatures, so casts of this form are sometimes discovered.
Because of its conchoidal fracture, flint can be used to make bladed tools such as arrowheads and has been used in this manner since ancient times. Flint produces sparks when struck with carbon-steel and has been used as a fire-starter. Flint was also used with flintlock guns. The hammers of these firearms held a piece of flint and when the trigger was pulled the flint struck a steel plate, which ignited the powder and caused the gun to fire.
Many books have listed England as a source of flint. Germany and Denmark are also considered sources. Flint Ridge, Ohio contains the rock and I have found good specimens in central Kentucky. Based on what I understand, flint can be found in many other places, but I cannot name any other specific sources.

Aegirine: An Uncommon Common-Mineral

Aegirine is common, in fact it is a component in some types of rock, but good crystals are significantly rarer. These crystallize in the monoclinic system and look like tiny models of the Washington Monument. Aegirine is black, but it bears tinges of red, green or brown. Its vitreous luster gives it the shimmer that we associate with glass and quartz.
As is the case with many minerals aegirine was once known by a different name because it was not well-understood. Sweden’s famous chemist Jons Jacob Berzelius was the first to unlock the secrets of the mineral’s chemistry some time in the early 1800s. Once he had identified its chemical structure he changed the name from acmite to aegirine, naming it after the Norse sea-god Aegir. It was suggested that he name the new mineral after him self, but he refused the honor and for his humility I tip my hat to him.
As I said before aegirine is a common mineral, but collectable specimens are only found in a few places. These include: Malawi, Russia’s Kola Peninsula, Norway, Greenland, and Arkansas.
I hope that you’ve enjoyed this post about aegirine. For a mineral with no technological uses nor any applications in jewelry it is quite an interesting stone.

Marcasite: The Brother of Pyrite

Marcasite and pyrite have a great deal in common. In fact they are each composed of the same chemical! Read on and learn more about this fascinating mineral--the brother of pyrite.
Marcasite is a polymorph of the chemical iron sulfide, just like pyrite. (You can read more about polymorphs in my post Polymorphism: One Chemical Many Minerals published on this blog May 6, 2011) Marcasite is of a similar pale-yellow color and it shines with a metallic luster as does pyrite. It gets its name from the Arabic word for pyrite and jewelers still call pyrite “marcasite.”
If there are these many similarities between the two minerals then how on earth can anyone tell them apart? Well, it has been difficult. It wasn’t until the 1800s that anyone could differentiate the two. There are some characteristics that are different, though. For starters marcasite has a different crystal shape than pyrite. Pyrite crystals are cubic whereas marcasite’s are orthorhombic. Now, when its crystals twin they can look like spears. Marcasite can also form in bladed, tabular, prismatic, massive, botryoidal, nodular, and stalactitic habits as well as “cockscombs” which look like the combs on chickens’ heads. Unless a marcasite specimen has very well-formed crystals it can still be a challenge to differentiate it from pyrite. Fortunately marcasite’s streak is a little different (read more about the streak test in my Nov. 1, 2010 post Pyrite the Imposter) Marcasite’s streak is greenish brown whereas pyrite’s is greenish black. Marcasite also exhibit’s a sulfur smell, which, as far as I know, pyrite does not.
There is one property that marcasite exhibits that pyrite does not, which I find rather unfortunate. Marcasite is unstable and will decay in the air. How fast it decays depends a lot upon how pure the sample is and how it is stored and handled. I keep mine in an air-tight container with a moisture-absorber, but so far no one has found a way to keep them from decaying indefinitely.
Marcasite is found in such places as: the Czech Republic, France, Greece, Belgium, Russia, Peru, Mexico, Peru, Japan, and the U.S. states of Michigan, Oklahoma, Wisconsin, Pennsylvania, Arkansas, and Illinois.
I hope that you enjoyed today’s post about pyrite’s brother marcasite. Next time I plan to write about marcasite’s unfortunate decaying problem.