Guide to minerals: Selenite

Jerrod Gallup (USA) I got this selenite crystal at the first Pebble Pups meeting I attended. As a result, I researched this crystal and found lots of interesting facts, in particular, that it was very unique. This particular crystal was found in Oklahoma in 1970. In fact, you can go to Oklahoma and find selenite crystals on the salt plains there and the hourglass-shaped selenite crystals are only found at this location. It is also the Oklahoma State Crystal. Fig. 1. Selenite crystal from Oklahoma.Image by Jerrod Gallup, 2013. Facts on fileFormula: CaSO4 2H2OCategory: Sulphate mineralCrystal system: MonoclinicMohs hardness scale: 2Lustre: PearlyStreak: WhiteColour: Can be green, brownish, yellow, greenish, gray green or gray whiteSelenite crystals are found in: Mexico and OklahomaHaiku An orange crystal Formed by nature’s loving hands In the soft brown ground. About the author Fig. 2. The author, Jerrod Gallup, is on the left. His cousin, Noah Paul, is on the right. They are collecting rock and mineral specimens in one of the areas of Colorado that were recently burned in a fire. Jerrod Gallup (age 9) is a third grader at Columbine Elementary School, Woodland Park, CO. He belongs to the Lake George Gem and Mineral Club. Further reading http://en.wikipedia.org/wiki/Selenite_(mineral). http://www.statesymbolsusa.org/Oklahoma/stateCrystalOklahoma.html.

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Crystals and minerals of the London Clay

Bob Williams (UK) I developed a passion for crystals while collecting fossils. To me, crystals don’t have to be fancy, rare or expensive to be of immense interest. Even a good specimen of the commonly encountered “fools gold” (iron pyrite, more technically referred to as iron sulphide) will be of great interest to me. I live in south-east England, which is perhaps not the best place in the country for collecting interesting crystal specimens. However, I have a special interest in a geological deposit known as “London Clay” that is highly fossiliferous and includes fossils of crabs and lobsters. Many people will not associate this deposit with interesting minerals, but this would be to underestimate its potential. Fig. 1. London Clay, Isle of Sheppey, Kent. Crystal groups display the geometry of the crystal structure that is associated with a particular mineral and their forms can vary a great deal. The atoms, from which a substance is built, combine into structures known as “unit cells”. The atomic structure of a unit cell is then identically repeated, forming assemblies that give rise to the final crystalline form (that is, the mineral itself). Some compounds produce small, crystalline structures while others can produce individual crystals that are massive in size and striking in overall appearance. Amethyst is a good example of this and is, perhaps, the most familiar and most commercially available mineral of this type. A closer look at the crystal structure of any mineral will reveal objects of such incredible, geometric … Read More

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