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| Black and white streak plates showing colored streaks for pyrite and rhodocrosite on black & white streak plates |
One of the most important tools in the arsenal used for
mineral identification is the streak plate.
This aid to mineral identification is usually a piece of unglazed
porcelain. The two colors most commonly used are black and white with white
used for dark colored minerals, and black used for light colored minerals.
Black colored stones are often called touchstones for
testing gold that leaves a golden colored streak that when treated with nitric
acid can be used to tell the karat of the gold being tested. If you draw a line with gold on a black piece
of unglazed porcelain it leaves a golden streak that can be tested by applying
different concentrations of nitric acid to the streak thereby finding its karat
or quality. 24 karat gold is unaffected
by the acid, but as the amount of gold in a sample decreases you are able to
determine how much gold there actually is in the sample. Different karat values have different
colors. For ages this was the definitive
test for gold but it has been replaces by more accurate tests based on
electronics. In the test 24 karat gold
is unaffected, but lesser grades of gold show increased chemical activity.
The black streak plate is used for testing for other
precious metals belonging to the platinum group metals (PGM). In most cases it is used to test light
colored minerals. Conversely the white
colored streak plate is used for testing light colored minerals.
For our prospecting and mineral collector friends we have
made available a streak testing kit composed of one each black and white 2”x 2”
test plates for $10.95
Individual streak plates are available for $5.75 each.
They can be ordered online with instructions for their use
included.
Full set black and white: $10.95
Full set black and white: $10.95
Bullion Exchanges is a well known Bullion Seller established in New York City's Diamond District.
ReplyDeleteBullion Exchanges have a wide variety of items like, precious metals that range from the popular gold and silver to the newly emerging platinum & palladium.
Bullion Exchanges are offering an enormous selection of products appealing to 1st time buyers and for seasoned collectors.