Minerals that show this include: bornite Cu 5 FeS 4 , hematite Fe 2 O 3 , sphalerite ZnS , and some specimens of labradorite plagioclase. Minerals that light up when exposed to ultraviolet light, x-rays, or cathode rays are called fluorescent. If the emission of light continues after the light is cut off, they are said to be phosphorescent. Some specimens of the same mineral show fluorescence while other don't. For example some crystals of fluorite CaF 2 show fluorescence and others do not.
Other minerals show fluorescence frequently, but not always. Magnetic minerals result from properties that are specific to a number of elements.
Minerals that do not have these elements, and thus have no magnetism are called diamagnetic. Examples of diamagnetic minerals are quartz, plagioclase, calcite, and apatite. Minerals that contain these elements may be weakly magnetic and can be separated from each other by their various degrees of magnetic susceptibility.
These are called paramagnetic minerals. Paramagnetic minerals only show magnetic properties when subjected to an external magnetic field. When the magnetic field is removed, the minerals have no magnetism. Ferromagnetic minerals have permanent magnetism if the temperature is below the Curie Temperature.
These materials will become magnetized when placed in a magnetic field, and will remain magnetic after the external field is removed. Other Properties Other properties that may be diagnostic include chatoyancy, asterism, piezoelectricity, and taste. Familiarize yourself with the meanings of these terms.
And watch for these properties as you examine minerals. Tables for Identification of Minerals. Beginning on page of the Text by Klein and Dutrow are determinative tables which should aid you in using physical properties of minerals to identify them. Note that the tables are broken first into two different groups based on Luster.
Within each group, the minerals are then further divided on the basis of streak, hardness, and cleavage. In the remarks column are listed other useful diagnostic property for each mineral.
Again, I encourage you to develop a systematic approach to identifying minerals. Questions from this material that could be asked on an exam. The use of physical properties to identify minerals will be necessary for the second lab exam, so you should become very familiar with using physical properties and the mineral identification charts to identify hand specimens of minerals.
Other example questions that could appear on the lecture midterm are as follows:. Physical Properties of Minerals. Crystal Habit In nature perfect crystals are rare.
Some common crystal habits are as follows discussed previously : Individual Crystals Cubic - cube shapes Octahedral - shaped like octahedrons, as described above. Groups of Distinct Crystals Dendritic - tree-like growths. Cleavage, Parting, and Fracture Cleavage Crystals often contain planes of atoms along which the bonding between the atoms is weaker than along other planes. Parting Parting is also a plane of weakness in the crystal structure, but it is along planes that are weakened by some applied force.
Fracture If the mineral contains no planes of weakness, it will break along random directions called fracture. Conchoidal fracture - breaks along smooth curved surfaces. Fibrous and splintery - similar to the way wood breaks. Hackly - jagged fractures with sharp edges. Uneven or Irregular - rough irregular surfaces. Hardness Hardness is determined by scratching the mineral with a mineral or substance of known hardness.
Common Objects. Two minerals of note have differences in hardness depending on direction: Kyanite has a hardness of 5 parallel to the length of the crystal, and a hardness of 7 when scratched along a direction perpendicular to the length. Tenacity Tenacity is the resistance of a mineral to breaking, crushing, or bending. Density Specific Gravity Density refers to the mass per unit volume. Specific gravity can usually be qualitatively measured by the heft of a mineral, in other words those with high specific gravities usually feel heavier.
Most common silicate minerals have a specific gravity between about 2. These would feel light compared to minerals with high specific gravities.
Color Color is sometimes an extremely diagnostic property of a mineral, for example olivine and epidote are almost always green in color. Streak Streak is the color produced by a fine powder of the mineral when scratched on a streak plate. Luster Luster refers to the general appearance of a mineral surface to reflected light.
Non-metallic - Non metallic lusters are referred to as vitreous - looks glassy - examples: clear quartz, tourmaline resinous - looks resinous - examples: sphalerite, sulfur. Play of Colors Interference of light reflected from the surface or from within a mineral may cause the color of the mineral to change as the angle of incident light changes.
Fluorescence and Phosphorescence Minerals that light up when exposed to ultraviolet light, x-rays, or cathode rays are called fluorescent. A mineral that naturally breaks into perfectly flat surfaces is exhibiting cleavage. Not all minerals have cleavage. A cleavage represents a direction of weakness in the crystal lattice. Cleavage surfaces can be distinguished by how they consistently reflect light, as if polished, smooth, and even. The cleavage properties of a mineral are described in terms of the number of cleavages and, if more than one cleavage, the angles between the cleavages.
The number of cleavages is the number or directions in which the mineral cleaves. A mineral may exhibit cleavage surfaces parallel to each other. Those represent a single cleavage because the surfaces are all oriented in the same diretion. The possible number of cleavages a mineral may have are 1,2,3,4, or 6. To see mineral cleavage, hold the mineral up beneath a strong light and move it around, move it around some more, to see how the different sides reflect light.
A cleavage direction will show up as a smooth, shiny, evenly bright sheen of light reflected by one set of parallel surfaces on the mineral. One reason gemstones are beautiful is that the cleavage planes make an attractive crystal shape with smooth faces. Fracture is a break in a mineral that is not along a cleavage plane. Fracture is not always the same in the same mineral because fracture is not determined by the structure of the mineral. Minerals may have characteristic fractures figure 9.
Metals usually fracture into jagged edges. If a mineral splinters like wood, it may be fibrous. Some minerals, such as quartz, form smooth curved surfaces when they fracture. All minerals have fracture. Fracture is breakage, which occurs in directions that are not cleavage directions. Some minerals, such as quartz, have no cleavage whatsoever.
When a mineral with no cleavage is broken apart by a hammer, it fractures in all directions. Quartz is said to exhibit conchoidal fracture. Conchoidal fracture is the way a thick piece of glass breaks with concentric, curving ridges on the broken surfaces. However, some quartz crystals have so many flaws that instead of exhibiting conchoidal fracture they simply exhibit irregular fracture. Irregular fracture is a standard term for fractures that do not exhibit any of the qualities of the other fracture types.
In introductory geology, the key fracture types to remember are irregular, which most minerals exhibit, and conchoidal, seen in quartz. All minerals are crystalline, but only some have the opportunity to exhibit the shapes of their crystals, their crystal forms. Many minerals in an introductory geology lab do not exhibit their crystal form. The shape of a crystal follows the symmetry of its crystal lattice. Quartz, for instance, forms six-sided crystals, showing the hexagonal symmetry of its crystal lattice.
There are two complicating factors to remember here: 1 minerals do not always form nice crystals when they grow, and 2 a crystal face is different from a cleavage surface. A crystal face forms during the growth of the mineral. A cleavage surface is formed when the mineral is broken. There are some properties that only help to distinguish a small number of minerals, or even just a single mineral. Calcite fizzes or effervesces as the HCl solution dissolves it and creates CO 2 gas.
Calcite is easy to identify even without testing the reaction to HCl, by its hardness, luster and cleavage. Another special property is magnetism. This can be tested by seeing if a small magnet responds to the mineral. The most common mineral that is strongly magnetic is the mineral magnetite. A special property that shows up in some sample of plagioclase feldspar is its tendency to exhibit striations on cleavage surfaces. Striations are perfectly straight, fine, parallel lines.
Magnification may be required to see striations on plagioclase cleavage surfaces. Other special properties may be encountered on a mineral to mineral basis.
Some minerals have other unique properties, some of which are listed in table 3. Hint: It is most likely found on your dinner table. Improve this page Learn More. Skip to main content.
The terms metallic and nonmetallic describe the basic types of luster. Table 7 lists the most common terms used to describe luster and an example of a corresponding mineral. Some minerals that don't exhibit luster are referred to as "earthy," "chalky," or "dull. One of the most obvious properties of a mineral is color.
Color should be considered when identifying a mineral, but should never be used as the major identifying characteristic. Streak is the color of the powdered mineral, which is usually more useful for identification than the color of the whole mineral sample. Rubbing the mineral on a streak plate will produce a streak. A streak plate can be made from the unglazed back side of a white porcelain bathroom or kitchen tile. Some minerals won't streak because they are harder than the streak plate.
Specific gravity is the ratio between the mass weight of a mineral and the mass weight of an equal volume of water. A mineral's specific gravity SG can be determined by dividing its weight in air by the weight of an equal volume of water.
For instance, quartz with a density of 2. The way in which a mineral breaks along smooth flat planes is called cleavage. These breaks occur along planes of weakness in the mineral's structure. However, if a mineral breaks along an irregular surface, it does not have cleavage.
When a mineral breaks irregularly, the breaks are called fractures.
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