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Zircon as a Gemstone
Zircon has been used as a gemstone for over 2000 years. Its very high dispersion and refractive index give it a brilliance and fire that rival those of diamond. For that reason, colorless faceted zircon has been used as both a popular and fraudulent substitute for diamond. Gemologists and many knowledgeable jewelers are able to distinguish…
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Geologic Occurrence Of Zircon
Zircon is a primary accessory mineral in most granitic rocks. It is also present in gneiss and other rocks derived from the metamorphism of zircon-bearing igneous rocks. Zircon is so common and widely distributed across the rocks of Earth’s surface that it could be considered to be a ubiquitous mineral. However, zircon is usually not noticed in rocks…
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What Is Zircon?
Zircon is a zirconium silicate mineral with a chemical composition of ZrSiO4. It is common throughout the world as a minor constituent of igneous, metamorphic, and sedimentary rocks. Zircon is a popular gemstone that has been used for nearly 2000 years. Today it serves as a modern birthstone for the month of December. Zircon occurs in a wide range of colors and has a brightness…
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Mineral Specimens as “Consumables”
Mineral specimens that are used properly in the science classroom or laboratory will need to be replaced frequently. Students will be investigating them with hardness tests, streak tests, acid tests and other experiments. All of these tests damage the specimen and make it less fit for the next group of students. To keep the acid…
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Sources of Hydrochloric Acid
Hydrochloric acid diluted to a 10% solution cannot be purchased in most communities. The best place to purchase commercially prepared solutions is from a laboratory supply company. Purchasing it ready-for-use is the recommended way to obtain it. Don’t try to prepare your own solution if you don’t know exactly what you are doing and have…
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Acid Bottle Selection
The type of bottle selected for dispensing the acid is important. Laboratory supply stores sell bottles that are designed for dispensing acid one-drop-at-a-time. The lid is always on these bottles (except when they are being cleaned or refilled), and they do not produce a spill when they are knocked over. Bottles with a removable lid…
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Limiting Frivolous Acid Use in Labs
Most students are intrigued with the acid test and want to try it. To limit frivolous acid use, students should be instructed to use a single drop of acid for the test and to only test specimens when carbonate minerals are suspected. If that is not done, some students will use the acid frivolously. This…
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Contamination in Mineral Identification Labs
When students are given minerals to identify, two situations can cause problems with their work. 1) In mineral identification labs, some students are ready to call any mineral that produces an acid reaction “calcite” or another carbonate. However, calcite is a ubiquitous mineral and it is often present as an intimate part of other mineral…
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The Acid Test on Rocks
LIMESTONE, DOLOSTONE, AND MARBLE Some rocks contain carbonate minerals, and the acid test can be used to help identify them. Limestone is composed almost entirely of calcite and will produce a vigorous fizz with a drop of hydrochloric acid. Dolostone is a rock composed of almost entirely of dolomite. It will produce a very weak fizz when a drop of cold…
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The Vigor of Carbonate Reactions
Careful observation is important because some carbonate minerals react vigorously and others barely react with cold acid. The carbonate mineral that is most commonly encountered by geologists is calcite (CaCO3). Calcite is a “ubiquitous” mineral. Ubiquitous means “found everywhere.” Calcite occurs in igneous, metamorphic, and sedimentary rocks and is the most commonly encountered carbonate mineral. If you place one…