How can a streak plate help you identify a mineral?

http://geology.about.com/od/mineral_ident/ig/streak/

A streak plate is a tool used in mineral identification. It is typically a small, flat piece of unglazed porcelain or ceramic tile. To use a streak plate, follow these steps:

1. Select the mineral specimen you want to identify. It should be a fresh surface, ideally a small fragment or a mineral with a rough surface.

2. Hold the streak plate firmly in one hand.

3. Take the mineral sample and firmly press it against the streak plate, applying enough pressure to leave a mark. You may need to scrape the mineral against the plate back and forth a few times to obtain the desired result.

4. Observe the color of the mineral's streak left on the streak plate.

Now, let's explain how the streak plate helps identify minerals:

The color of a mineral's streak refers to the color of the powdered form of the mineral. Sometimes, it differs from the color of the mineral itself. The streak color can provide valuable information for mineral identification and help differentiate between similar-looking minerals.

Here's how it works:

1. Metallic minerals: These minerals typically leave a streak that is the same color as the mineral. For example, if a mineral leaves a reddish-brown streak, it is likely to be a metallic mineral with a reddish-brown color.

2. Non-metallic minerals: These minerals often leave a streak that is not necessarily related to their mineral color. For example, a mineral with a green color might leave a white streak. This contrast indicates that the mineral is non-metallic and not primarily green.

By comparing the observed streak color to known streak colors of various minerals, you can narrow down the possibilities and make an educated guess about the mineral's identity.

It is important to note that streak plates can sometimes be too soft to scratch harder minerals, causing the streak to be colored by the plate itself. In such cases, it's recommended to use a streak plate with a higher Mohs hardness rating or a different mineral identification test.