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What characteristics does Porcelain possess that makes it a good choice for the Streak test? Additionally, are there any other materials that could also be used for designing a Streak plate?

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  1. It's white, so the streak colour is obvious.
  2. It's hard. Porcelain is made from aluminosilicates like sillimanite and mullite. Mohs hardness is around 7. Not many geological materials are harder than it, and streak is not a diagnostic feature for those that are harder.
  3. It's rough (i.e. unglazed) so it's really good in breaking tiny fragments from the tested material, thus producing the streak.
  4. It's cheap and widely available.
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    $\begingroup$ Thank you for the quick reply! Would you also happen to know of other materials that fulfil all or most of your above mentioned criteria and could thus be a good choice as well, or is the popularity of Porcelain so overarching that there is no need for any alternative? $\endgroup$ – vshlrnjth Mar 30 '18 at 19:34
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    $\begingroup$ @vshlrnjth frosted glass maybe? But porcelain is cheaper and not as brittle. Another option could be “porcelain” made of pure alumina, but I don’t think they would be as cheap and widely available as aluminosilicate porcelain. $\endgroup$ – Gimelist Mar 31 '18 at 4:44
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    $\begingroup$ you can use a ceramic wetstone but this is expensive and the color can be a problem. $\endgroup$ – trond hansen Mar 31 '18 at 6:21
  • $\begingroup$ You can also use a hammer to pound the specimen to a powder then look at it on a white piece of paper $\endgroup$ – haresfur Apr 2 '18 at 22:06

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