Question

How can a mineral be identified using its physical properties?

Short answer

Use color, streak, hardness, luster, cleavage/fracture, and special properties to identify minerals.

Step-by-step solution

Examine Color

Observe the color of the mineral. While color can be a helpful identifier, it is not always reliable due to impurities that might alter a mineral's natural color.

Check Streak

Perform a streak test by rubbing the mineral against a piece of unglazed porcelain to observe the color of the streak it leaves. This can be more reliable than the mineral's surface color.

Measure Hardness

Use the Mohs scale of hardness to scratch the mineral with standard objects or other minerals to determine its hardness level, which ranges from 1 (talc) to 10 (diamond).

Observe Luster

Examine how the mineral reflects light, known as its luster. This can be metallic, glassy, dull, etc., and gives insight into the mineral's surface properties.

Determine Cleavage and Fracture

Inspect how the mineral breaks. Cleavage refers to how a mineral breaks along flat planes, while fracture describes an uneven, rough break.

Consider Other Properties

Identify any special properties, such as magnetism, reaction to acid, or specific gravity, which could provide additional confirmation of the mineral's identity.

Key concepts

Physical Properties of Minerals

Physical properties are core attributes that help in identifying minerals. These include color, luster, hardness, streak, cleavage, and fracture. By examining these characteristics, geologists can differentiate minerals. It's important to note that while some properties, like color, are visual, others require specific tests. Since visual properties can sometimes be altered by impurities, it's crucial to use a combination of different tests for accurate identification.

Mohs Scale of Hardness

The Mohs scale of hardness is a standard method used to determine a mineral's hardness, ranging from 1 to 10.
Developed by Friedrich Mohs in 1812, this scale helps identify minerals based on their ability to scratch or be scratched by another mineral.
- Talc, with a hardness of 1, can easily be scratched by all minerals. - Diamond, rated 10 on the scale, scratches all other minerals. Hardness testing is crucial because it remains consistent despite the mineral's appearance changes.

Mineral Streak Test

The mineral streak test involves rubbing a mineral on an unglazed porcelain plate to observe the color of its powder. This color, known as the streak, is usually more reliable than the mineral's external color because it remains unchanged by surface impurities.
This test is especially helpful for identifying minerals with a metallic luster, as their streak often differs significantly from the surface color.

Mineral Luster

Luster describes how a mineral reflects light. This property is not only about shine but also about the kind of surface a mineral has.
- Metallic luster indicates a shiny, metal-like surface. - Non-metallic luster might be glassy, pearly, or dull. Identifying luster helps narrow down the mineral type because it provides clues about the mineral's composition and structure.

Cleavage and Fracture in Minerals

Cleavage and fracture refer to the manner in which a mineral breaks. - **Cleavage** is when a mineral breaks along smooth, flat planes. This property varies from mineral to mineral and provides significant identification clues. - **Fracture**, on the other hand, describes an irregular break, often rough and uneven. Understanding a mineral's cleavage and fracture patterns aids in determining its identity and also in predicting how a mineral will behave when struck or weathered.