Topaz (8), corundum (9), and diamond (10).
Those minerals that are harder than the unglazed porcelain streak plate will scratch it rather than leave a streak.
The streak test works only on minerals softer than porcelain because it relies on the ability of a mineral to leave a colored mark or powder on a porcelain plate. If a mineral is harder than porcelain, it won't leave a streak, as it cannot scratch the surface. Porcelain typically has a hardness of about 6 on the Mohs scale, so only minerals with a hardness less than this can effectively produce a streak. This property helps in identifying minerals based on their color and texture.
You can determine the streak of a mineral whose Mohs scale is higher than the streak plate by either filing or crushing with a hammer before rubbing the sample on a streak plate.
A streak plate on the Mohs scale is a piece of unglazed porcelain used to determine the color of a mineral in powdered form. By rubbing the mineral against the streak plate, it leaves a streak that can be compared to the standard colors on the scale to identify the mineral.
A mineral that can scratch glass but not a streak plate is quartz. Quartz has a hardness of 7 on the Mohs scale, which allows it to scratch glass (which has a hardness of about 5.5) but is harder than the streak plate, typically made from porcelain, which has a hardness of around 6-7. Therefore, while quartz can leave scratches on glass, it will not produce a streak on a streak plate.
Two minerals that do not leave a streak on a streak plate are quartz and fluorite. Both minerals have a hardness higher than that of the streak plate, so they will not leave a streak when rubbed against it.
Those minerals that are harder than the unglazed porcelain streak plate will scratch it rather than leave a streak.
Minerals with a hardness greater than around 7 on the Mohs hardness scale will not leave a streak on a standard unglazed porcelain streak plate. They will instead scratch and powder the streak plate.
Diamond will not leave a streak on a porcelain streak plate because diamond is harder than the streak plate. It will leave a scratch on the streak plate for the same reason.
Gold and pyrite leave a streak because they are both metallic minerals, which means they can rub off on a streak plate, leaving a colored line that reflects their metallic composition. In contrast, quartz is a non-metallic mineral with a hardness of 7 on the Mohs scale, making it too hard to leave a streak when rubbed against a streak plate. As a result, quartz typically does not produce a streak.
It leaves a scratch instead of a streak because Topaz has a higher number on the Moh's scale compared to the streak plate.
A streak test is not used to identify minerals with a hardness greater than 7 on the Mohs scale, as these minerals can scratch the streak plate. Additionally, streak tests may not be effective for identifying minerals that have a streak color similar to the streak plate itself.
Quartz does not leave a streak behind when rubbed against a streak plate. This is because quartz has a hardness of 7 on the Mohs scale, making it harder than the streak plate, which is typically made of porcelain and has a hardness of around 6. As a result, quartz will not produce a colored streak and will instead leave a scratch on the plate.
The streak test works only on minerals softer than porcelain because it relies on the ability of a mineral to leave a colored mark or powder on a porcelain plate. If a mineral is harder than porcelain, it won't leave a streak, as it cannot scratch the surface. Porcelain typically has a hardness of about 6 on the Mohs scale, so only minerals with a hardness less than this can effectively produce a streak. This property helps in identifying minerals based on their color and texture.
Topaz is a hard mineral, ranking 8 on the Mohs scale of hardness, so it is harder than most common materials used to test streak. Since streak tests are typically performed on softer minerals, such as using a porcelain streak plate with a hardness of about 6.5, the topaz does not leave a streak because it is harder than the material being used for the test.
When identifying minerals, having no streak is a property of hardness. A streak plate has a hardness of ~7(Moh's Scale). Thus any mineral having a hardness greater than 7 will have no streak.Metallic is the description of luster. Or the general appearance of a mineral surface in reflected light.If you were refering to the mineral having metal elements in it, streak is actually very useful for identifying them. Many minerals that are composed of non-metals have a white streak which can appear to be no streak, however there are also many minerals with no streak which are composed of non-metallic minerals (Diamond).
Diamond is the only mineral that can scratch glass but not leave a streak on a streak plate. Glass has a hardness of around 5.5 on the Mohs scale, while a streak plate typically has a hardness of around 6.5. Diamond, with a hardness of 10, is able to scratch glass but not the streak plate.