One of the things mineralogists must do is identify and categorize minerals. While a mineralogist might use a high-powered microscope to identify some minerals, most are recognizable using physical properties. Figure 1. This mineral has shiny, gold, cubic crystals with striations, so it is pyrite. Check out the mineral in figure 1. What is its shape?
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Are the individual crystals shiny or dull? Are there lines striations running across the minerals? In this lesson, the properties used to identify minerals are described in more detail.
Mineral Detection and Identification
Diamonds are popular gemstones because the way they reflect light makes them very sparkly. Turquoise is prized for its striking greenish-blue color. Notice that specific terms are being used to describe the appearance of minerals. Color is rarely very useful for identifying a mineral. Different minerals may be the same color. Real gold, as seen in figure 2, is very similar in color to the pyrite in figure 1. Figure 2. This mineral is shiny, very soft, heavy, and gold in color, and is actually gold. The same mineral may also be found in different colors.
Figure 3 shows one sample of quartz that is colorless and another quartz that is purple. A tiny amount of iron makes the quartz purple. Many minerals are colored by chemical impurities.
Figure 3. Purple quartz, known as amethyst, and clear quartz are the same mineral despite the different colors.
Streak is a more reliable property than color because streak does not vary. Minerals that are the same color may have a different colored streak.
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Many minerals, such as the quartz in the figure 3, do not have streak. To check streak, scrape the mineral across an unglazed porcelain plate Figure 4. Yellow-gold pyrite has a blackish streak, another indicator that pyrite is not gold, which has a golden yellow streak. Figure 4.
The streak of hematite across an unglazed porcelain plate is red-brown. View details. Flag as inappropriate. See more. Geology Toolkit Premium. Andrei Ionut Apopei.
Mineral Detection and Identification
Understanding Geology. Discover Minerals, Rocks, Fossils. Essentials of Geology. Unfortunately, it can also be the hardest to determine sorry. There are two 2 major subdivisions: fracture and cleavage. Fracture: The mineral just breaks, leaving an uneven surface. Most are irregular but there are some special cases ex: the conchoidal fractures common to quartz and glass. Cleavage: The mineral splits along closely spaces parallel planes, leaving a mirror surface which will flash at you if rotated in the light.
Cleavage is controlled by the internal crystalline order of the mineral. A mineral can have 1 , 2, 3 , 4, or 6 planes of cleavage. If more than one 1 plane is present, it is important to note the angles between the cleavages. Cleavage can be obscured, but is diagnostic when present. Terms such as Perfect, Good in 2 directions, Poor, etc. Cleavage can be tough to distinguish from external crystalline form, and it's always a shame to break a good "crystal" when checking for cleavage.
This is almost impossible to measure in the field, but a rough approximation can be determined. Effervescence the Fizz test : Minerals containing calcium carbonate CaCO 3 will generally react when exposed to weak acid usually hydrochloric acid HCl , but even vinegar will work. Carbon dioxide CO 2 is released and the mineral or rock literally "fizzes. Magnetism: Magnetite is naturally magnetic. Don't put a chunk near your computer!
Taste: Some minerals have a distinctive taste. Notable examples include Halite rock salt , and Chalcanthite a copper sulfate - be careful with this one!! I don't generally recommend the taste test.
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