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 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 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.
.jpg)
.jpg)
.jpg)
.jpg)