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Sunday, July 8, 2012

Streak Plates for Mineral Identification

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 

Streak Plate Set (B and W)


Single black streak plate $5.75: 

Black Streak Plate


Single white streak plate $5.75: 

White Streak Plate


Connecticut residents please add 6.35% sales tax.

Shipping is included on all orders.

From time to time we will be adding other items useful for the mineral collector or prospector.

Photo by Ra'ike

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