Steak is a colour of a mineral when powdered and observed against unglazed porcelain (white ceramic plate). Streak plates that have been used rigorously will be laminated with streaks and powdered minerals. However, they can easily be cleaned with water and damp or dry 220 grit sandpaper. In addition, Aluminum oxide or silicon carbide sandpaper works best to clean streaks since the granules are hard enough to smoothen out the surface of the streak plate. The sanding should be carried out wet to control dust.
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How to Determine the Colour of the Streak?
A "streak test" is conducted to identify the colour of a mineral in its powdered form. The colour of a mineral's powder is commonly a very crucial property for determining the mineral.
How is a Streak Test Conducted?
The streak test is carried out scraping a specimen of the mineral covering the piece of unglazed porcelain termed as a "streak plate." The streak test should be undertaken on clean, unworn, or freshly broken specimens of the mineral. This is conducted in order to minimize the possibility that a foreign matter, pollutant, weathered coating, or corrosion will influence the outcome of the test.
This can yield a little amount of powdered mineral on the surface of the plate. The powder colour of that mineral is what we call a "streak."
Streak Colours of Common Minerals
Uses of Streak Plates
Additionally to their usage in conducting the streak test, streak plates can be used any time you require a little amount of powdered mineral. In performing the acid test to differentiate calcite from dolomite, dolomite might need powdering in order to exhibit effervescence with dilute hydrochloric acid. Simply use the streak plate in order to create some powder of your specimen and add a small amount of acid to it right on the streak plate. For this test, a black streak plate makes monitoring easier since powdered dolomite is white.
A few minerals will yield a stench (odour) upon being powdered or fragmented. For example, sphalerite releases an odour of sulfur when it is powdered or broken. Scraping it across a streak plate is the easiest way to undertake this test.
Traces to other mineral properties can be acquired while conducting the streak test. Minerals harder than the streak plate are rapidly determined. Experienced testers can approximate the hardness of a specimen by how complicated it is to mark the streak plate. augite often displays its splintery cleavage, olivine most commonly exhibits its granular characteristic, and black tourmaline displays its brittleness. Having said that When you conduct a streak test, look for just beyond the colour of a specimen's powder.
Rubbing the mineral across an unglazed porcelain white plate determines and describes the colour of the powder left on the plate, i.e. the streak.
Mineral pyrite is gold-coloured, however, its streak is greenish-black.
Most transparent and pale coloured or translucent minerals have a non-identifying white streak.
Minerals having a hardness of above 6.5 will not display a streak since they are harder than a piece of unglazed porcelain.