Done by scraping the mineral across an unglazed porcelain streak plate.Article by: Hobart M. King, PhD, RPG

The Streak Test: Marks, recognized as "streaks," are created by scraping mineral specimens across unglazed porcelain plates. ~ above the left, a specimen that pyrite has developed a black streak. On the right, a specimen of rhodochrosite has developed a white streak. Numerous minerals produce a white streak, and some geologists choose using a black streak plate for these minerals since the mineral particles in the streak are less complicated to observe. This photo by Ra"ike is used right here under a GNU Free document License.

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What is the Streak Test?

The "streak test" is a an approach used to recognize the shade of a mineral in powdered form. The shade of a mineral"s powder is often a really important property for identifying the mineral.

The streak check is done by scraping a specimen of the mineral throughout a item of unglazed porcelain well-known as a "streak plate." This can create a little amount that powdered mineral top top the surface ar of the plate. The powder shade of the mineral well-known as that is "streak."

Streak color of typical Minerals
Andalusite White or colorless (hardness is around the exact same as the streak plate).
Anhydrite White.
Apatite White.
Arsenopyrite Dark grayish black.
Augite White come greenish gray. Augite can be splintery and close come the hardness the the streak plate, therefore brittle fragments, fairly than a powder, will occasionally be produced.
Azurite Light blue.
Barite White.
Bauxite White. Regularly discolored come pink, brown, or red by steel staining.
Benitoite White.
Beryl Colorless (harder 보다 the streak plate).
Biotite White to gray (don"t it is in deceived by flakes).
Bornite Grayish black.
Calcite White.
Cassiterite Colorless.
Chalcocite Grayish black.
Chalcopyrite Greenish black.
Chlorite Greenish to greenish-black to white.
Chromite Dark brown.
Chrysoberyl Colorless (harder 보다 the streak plate).
Cinnabar Red.
Clinozoisite White.
Copper Metallic copper red.
Cordierite Colorless (harder than the streak plate).
Corundum Colorless (harder 보다 the streak plate).
Cuprite Brownish red.
Diamond Colorless (harder than the streak plate).
Diopside White to irradiate green.
Dolomite White.
Enstatite White come gray.
Epidote White or colorless (about the same hardness as the streak plate).
Euclase White or colorless (when harder than the streak plate).
Fluorite White.
Fuchsite White (often sheds tiny green mica flakes).
Galena Lead gray to black.
Garnet Colorless (harder 보다 the streak plate).
Glauconite Dull green.
Gold Metallic gold yellow.
Graphite Black.
Gypsum White.
Halite White.
Hematite Red to red brown.
Hornblende White. Brittle, often leaves black cleavage debris behind instead of a streak.
Ilmenite Black.
Jadeite Colorless (harder 보다 the streak plate).
Kyanite White or colorless (about the same hardness together the streak key in one direction).
Limonite Yellowish brown.
Magnesite White.
Magnetite Black.
Malachite Green.
Marcasite Grayish Black.
Molybdenite Bluish gray, gray.
Monazite White.
Muscovite White, regularly sheds small cleavage flakes.
Nepheline White.
Nephrite Colorless (harder than the streak plate).
Olivine White or colorless (about the same hardness together the streak plate). Often sheds tiny granules rather of a powder.
Orthoclase White.
Plagioclase White.
Prehnite White.
Pyrite Greenish black color to brownish black.
Pyrophyllite White.
Pyrrhotite Grayish black.
Quartz Colorless (harder 보다 the streak plate).
Rhodochrosite White.
Rhodonite White.
Rutile Pale brown.
Scapolite White.
Serpentine White.
Siderite White, an extremely light brown.
Sillimanite White or colorless (about the exact same hardness as the streak plate).
Silver Silvery white.
Sodalite White or light blue.
Sphalerite White come yellowish brown, frequently with an smell of sulfur.
Spinel Colorless (harder than the streak plate).
Spodumene White or colorless (about the exact same hardness together the streak plate).
Staurolite Colorless (harder than the streak plate).
Sulfur Yellow.
Sylvite White.
Talc White come pale green.
Titanite White.
Topaz Colorless (harder than the streak plate).
Tourmaline Colorless (harder 보다 the streak plate). Specimens frequently fracture, shedding small particles.
Turquoise White, greenish, bluish.
Uraninite Brownish black, grayish.
Vanadinite Pale yellow to yellowish brown.
Witherite White.
Wollastonite White.
Zircon Colorless (harder 보다 the streak plate).
Zoisite White.

How to conduct the Streak Test

The streak test should be done on clean, unweathered, or freshly broken specimens that the mineral. This is done to minimize the opportunity that a contaminant, weathered coating, or tarnish will influence the outcomes of the test.

The preferred method for conducting a streak test is to choose up a representative specimen of the mineral with the hand that you write with. Select a representative point or protrusion on the specimen that will be scraped throughout the streak plate. Through your other hand, place the streak plate level on a tabletop or laboratory bench. Then, when holding the streak bowl flat and also firmly in place on the tabletop, place the allude of the specimen firmly versus the streak plate, and, while maintaining firm pressure, traction the specimen across the plate. Currently examine the streak to determine its color and also to confirm that it is a powder, instead of grains, splinters, or broken pieces.

Don"t be Wimpy!

The most usual error do by people who room doing the streak test for the very first time is to lightly obstacle the specimen back and soon on the surface ar of the streak plate. This will not create a suitable streak. Some mineral specimens room so hard that very firm pressure and determination are forced to develop a mineral powder.

Related: Mohs Hardness Testing

Why use the Streak Test?

The streak check is valuable because plenty of minerals take place in a selection of obvious colors - yet all specimens of that mineral re-publishing a similar streak color. For example: specimens of hematite have the right to be black, red, brown, or silver in color and occur in a wide range of habits; however, all specimens that hematite develop a streak with a red color. This is a an useful test because that hematite. It deserve to be supplied to distinguish hematite from a big number of other opaque minerals with a high specific gravity and comparable color and habit.

Fluorite is one more mineral where the evident color deserve to be different from the shade of the streak. Specimens the fluorite deserve to be green, yellow, purple, blue, or colorless. However, all specimens the fluorite have a white streak. Specimens of pyrite always have a brassy yellow color; however, all specimens that pyrite produce a black streak.

Related: The mountain Test

Don"t it is in Deceived!

A number of things can reason a streak check to offer unreliable results. To prevent problems, keep the adhering to items in mind.Always execute the streak test making use of a surface ar of the specimen that has not been weathered. Countless weathered specimens space coated v a great of modification products that have a various streak color. If you are in doubt and are allowed to break the specimen, experimentation on a freshly damaged surface is a great idea.Repeat the test utilizing two different parts the the specimen or two various pieces that the same product for confirmation.

Contamination transforms Streak:
This specimen the bauxite from Demerara, Guyana should have actually a white streak; however, it has actually a pinkish streak because it is contaminated by iron-staining. The streak likewise varies depending on what part of the specimen is tested. Specimen is roughly 4 customs (10 centimeters) across.

Some minerals are brittle or have a granular habit. When these space scraped across a streak plate, a trace of dislodged grains or damaged pieces are developed instead the a powder. Obstacle the tip of your index finger across the streak key to ar a little amount the the mineral flour on your finger tip. Then rub the tip of your index finger against the reminder of your thumb. A powder will have actually a smooth feel in between your finger and thumb. Brittle pieces or granules will certainly feel gritty. Streak color is established from a powder fairly than fragments.If the results of your streak test seem inaccurate, be cautious. The streak test need to be used as a "hint" resulting in the identification of a mineral. To know of a mineral should always be based upon monitorings of several different mineral properties.

Refreshing her Streak Plate

Streak key that have actually been used greatly will be extended with streaks and also powdered mineral. Lock can easily be cleaned with water and a piece of wet or dry 220 grit sandpaper. Aluminum oxide or silicon carbide sandpaper functions best due to the fact that the granules space hard enough to smooth the surface of the streak plate. The sanding have to be done wet to control dust.


The best way to learn around minerals is to study with a repertoire of tiny specimens that you have the right to handle, examine, and observe your properties. Cheap mineral collection are obtainable in the Store.

Other provides for Streak Plates

In enhancement to their use in doing the streak test, streak plates can be used any time you need a tiny amount the powdered mineral. In law the mountain test to distinguish calcite native dolomite, dolomite might require being powdered to show effervescence with dilute hydrochloric acid. Simply use the streak plate to make part powder of your specimen and add acid come it best on the streak plate. Because that this test, a black color streak key makes observation easier since powdered dolomite is white.

A couple of minerals will create an smell upon being broken or powdered. For example, sphalerite release an odor of sulfur once it is broken or powdered. Scraping it throughout a streak bowl is a convenient method to conduct this test.

Hints to other mineral properties deserve to be derived while act the streak test. Mineral harder 보다 the streak bowl are quickly identified. Proficient testers can estimate the hardness of a specimen by how challenging it is to mark the streak plate. Olivine frequently reveals the granular nature, augite often reveals that is splintery cleavage, and black tourmaline regularly reveals the brittleness. As soon as you do the streak test, watch for more than the shade of a specimen"s powder.

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