Gem Rocks

What is Corundum?

Corundum is a rock-forming mineral that is found in igneous, metamorphic, and sedimentary rocks. It is an aluminum oxide with a chemical composition of Al2O3 and a member of the trigonal crystal system.

The mineral is widely known for its extreme hardness and for the fact that it is sometimes found as beautiful transparent crystals in many different colors. The extreme hardness makes corundum an excellent abrasive, and when that hardness is found in beautiful crystals, you have the perfect material for cutting gemstones.

Natural and synthetic corundum are used in a wide variety of industrial applications because of their toughness, hardness, and chemical stability. They are used to make industrial bearings, scratch-resistant windows for electronic instruments, wafers for circuit boards, and many other products

Fluorite

Fluorite (CaF2) is considered to be one of the most colorful minerals in the world. Common colors of fluorite include purple, green, yellow, and blue. Flourite is also visible under ultraviolet light, a property that gets its name, flourescence, from the mineral. Fluorite is often mistaken for quartz but it has a lower hardness of 4. Fluorite is the state mineral of Illinois which was once the largest fluorite producer in the United States.

Calcite
Calcite is made of calcium carbonate (CaCO3). Generally white to clear, calcite is easily scratched with a knife. Due to the presence of carbonates (CO3), calcite reacts to most acids (such as hydrochloric acid, HCl) and effervesces on contact. Most seashells are made of calcite or related minerals. Calcite can be found in many cave and karst formations such as the calcite features at:

Jewel Cave National Monument, South Dakota

🤩the Munich Mineral Days with agates from the High Atlas, Morocco.❤️❤️

🤩🤩From mibladn Morocco,

One last agate from the wind turbine construction in 2001 on the Freisener Höhe, found by Christof Keller. It is one of the very best agates from there and has a respectable size of 17x9.5cm.

Agouim region, Morocco. Agate with a calcite twin, 12x9cm🤩

😍Every purchase in one purchase with one insulated center, Agouim Gebiet, Morocco, 16x13cm.

💯❤️Verkieseltes mit Chalcedoneinschlüssen vom "Blue Forest", Wyoming, USA (17x13x18cm). This yesterday's copy is one of the ends and the rest of the copies are left unused. Dadurch wurden diese vor der Verwitterung bewahrt. On the other side of the page and in the background, you will see the Chalcedonblasen text. Gekauft auf den Mineralientagen in München.
Literatur: Peter C. Huber, Mineralienwelt, 22.Jg., Heft 6, 2011, S. 98-104.