A porcelain streak plate has a relative hardness of about 6, so minerals with a hardness of 6 and above can not be tested on it as they will only scratch the streak plate.
| Streak Test | ||||||||||||||
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Streak is the color of a mineral powder. Many minerals have a different color when powdered than they do in crystal or massive forms. The color may be entirely different, or it may be a different shade. Quite a few minerals give a streak that is lighter in color than the whole crystal or massive pieces. A streak is usually obtained by dragging a sharp edge, grain, or point of a crystal across a streak plate – which is simply an unglazed piece of porcelain tile.
A porcelain streak plate has a relative hardness of about 6, so minerals with a hardness of 6 and above can not be tested on it as they will only scratch the streak plate. |
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| Pyrite with its greenish-black streak | ||||||||||||||
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| Hematite with its reddish streak | Galena with its dark grey-black streak | |||||||||||||