![]() Some minerals won't streak because they are harder than the streak plate. A streak plate can be made from the unglazed back side of a white porcelain bathroom or kitchen tile. Rubbing the mineral on a streak plate will produce a streak. Streak is the color of the powdered mineral, which is usually more useful for identification than the color of the whole mineral sample. ![]() Color should be considered when identifying a mineral, but should never be used as the major identifying characteristic. One of the most obvious properties of a mineral is color. Some minerals that don't exhibit luster are referred to as "earthy," "chalky," or "dull." Color Table 7 lists the most common terms used to describe luster and an example of a corresponding mineral. The terms metallic and nonmetallic describe the basic types of luster. Try to find an old, broken or worn flat file You may be able to get this cut at a local hardware store.) Tape the edges of the glass with duct tape. Window glass (2 inches square use caution making this scratch plate. All pieces in the hardness test kit should be compared to one another and specific minerals with a known hardness. Wear safety glasses and gloves when cutting class. Parents should help children make the kit. Scratched by a steel file (6.5) easily scratches glassĪ mineral hardness test kit can be easily created from common household or hardware items (table 6). Hardnessĭifficult to scratch by a nail (4) scratched easily by a knife (5)ĭifficult to scratch with a knife (>5) barely scratches glass (5.5) A fingernail has a hardness ranging from 2 to 2.5, a penny is a little harder than 3, window glass ranges from 5.5 to approximately 6 in hardness, and a knife blade is generally in the range of 5 to 6.5. Each higher-numbered (harder) mineral will scratch any mineral with a lower number (softer).Ī rough measure of mineral hardness can be made by assembling a kit of handy objects (table 6). The scale arranges the minerals in order of increasing hardness. Federick Mohs, a German mineralogist, produced a hardness scale (table 5) using a set of ten standard minerals. Hardness is determined by the ability of one mineral to scratch another. The ability to resist being scratched-or hardness-is one of the most useful properties for identifying minerals. Most minerals can be characterized and classified by their unique physical properties: hardness, luster, color, streak, specific gravity, cleavage, fracture, and tenacity.
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