Doodle Bob
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why are streak tests important? why are hardness tests important?
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why are streak tests important? why are hardness tests important?
- Thread starter Doodle Bob
- Start date
Streak Test:
The color of a mineral when it is powdered is called the streak of the mineral. Crushing and powdering a mineral eliminates some of the effects of impurities and structural flaws, and is therefore more diagnostic for some minerals than their color. Streak can be determined for any mineral by crushing it with a hammer, but it is more commonly (and less destructively) obtained by rubbing the mineral across the surface of a hard, unglazed porcelain material called a streak plate.
The color of the powder left behind on the streak plate is the mineral's streak. The streak and color of some minerals are the same. For others, the streak may be quite different from the color, as for example the red-brown streak of hematite, often a gray to silver-gray mineral. The combination of luster, color, and streak may be enough to permit identification of the mineral.
Hardness Test by The Mohs' Hardness Scale
A good property in mineral identification is one that does not vary from specimen to specimen. In terms of reliability, hardness is one of the better physical properties for minerals. Specimens of the same mineral may vary slightly, but generally they are quite consistent. Inconsistencies occur when the specimen is impure, poorly crystallized, or actually an aggregate and not an individual crystal.
Hardness is one measure of the strength of the structure of the mineral relative to the strength of its chemical bonds. Hardness is generally consistent because the chemistry of minerals is generally consistent.
Hardness can be tested through scratching. A mineral can only be scratched by a substance harder than itself. A hard mineral can scratch a softer mineral, but a soft mineral cannot scratch a harder mineral (no matter how hard you try). Therefore, a relative scale can be established to account for the differences in hardness simply by seeing which mineral scratches another. That is exactly what French mineralogist Friedrich Mohs proposed almost one hundred and seventy years ago. The Mohs' Hardness Scale, starting with talc at number 1 and ending with diamond at number 10, is universally used around the world as a way of distinguishing minerals. Simply put—the higher the number, the harder the mineral.
The color of a mineral when it is powdered is called the streak of the mineral. Crushing and powdering a mineral eliminates some of the effects of impurities and structural flaws, and is therefore more diagnostic for some minerals than their color. Streak can be determined for any mineral by crushing it with a hammer, but it is more commonly (and less destructively) obtained by rubbing the mineral across the surface of a hard, unglazed porcelain material called a streak plate.
The color of the powder left behind on the streak plate is the mineral's streak. The streak and color of some minerals are the same. For others, the streak may be quite different from the color, as for example the red-brown streak of hematite, often a gray to silver-gray mineral. The combination of luster, color, and streak may be enough to permit identification of the mineral.
Hardness Test by The Mohs' Hardness Scale
A good property in mineral identification is one that does not vary from specimen to specimen. In terms of reliability, hardness is one of the better physical properties for minerals. Specimens of the same mineral may vary slightly, but generally they are quite consistent. Inconsistencies occur when the specimen is impure, poorly crystallized, or actually an aggregate and not an individual crystal.
Hardness is one measure of the strength of the structure of the mineral relative to the strength of its chemical bonds. Hardness is generally consistent because the chemistry of minerals is generally consistent.
Hardness can be tested through scratching. A mineral can only be scratched by a substance harder than itself. A hard mineral can scratch a softer mineral, but a soft mineral cannot scratch a harder mineral (no matter how hard you try). Therefore, a relative scale can be established to account for the differences in hardness simply by seeing which mineral scratches another. That is exactly what French mineralogist Friedrich Mohs proposed almost one hundred and seventy years ago. The Mohs' Hardness Scale, starting with talc at number 1 and ending with diamond at number 10, is universally used around the world as a way of distinguishing minerals. Simply put—the higher the number, the harder the mineral.
M
mnrlboy
Guest
Many minerals look very similar, and sometimes the only reliable way to identify them is to test their physical and chemical properties. Streak and hardness tests tell you about the color of the powdered mineral, and about how tightly bonded the crystal structure is. This information can help identify minerals that may otherwise look similar.