Question

You have an unknown mineral that can scratch glass but cannot scratch a porcelain streak plate. What is its approximate hardness?

Short answer

The approximate hardness of the unknown mineral is around 6.5 on the Mohs Hardness Scale, as it can scratch glass (hardness 5.5) but not a porcelain streak plate (hardness 7).

Step-by-step solution

Mohs Hardness of Glass

Determine the Mohs hardness value for glass. Glass is typically around 5.5 on the Mohs scale.

Mohs Hardness of Porcelain Streak Plate

Determine the Mohs hardness value for a porcelain streak plate. A porcelain streak plate typically has a hardness of 7 on the Mohs scale.

Determine the Range for the Unknown Mineral's Hardness

The unknown mineral can scratch glass but not a porcelain streak plate. The mineral's hardness must be greater than the Mohs hardness value of glass (5.5) and less than the Mohs value of the porcelain streak plate (7).

Approximate Hardness of the Unknown Mineral

The approximate hardness of the unknown mineral is between 5.5 (harder than glass) and 7 (softer than porcelain streak plate). Given the limited information in the exercise, the best estimate for the hardness of the unknown mineral would be in the middle of this range. The approximate hardness of the unknown mineral is therefore around 6.5 on the Mohs Hardness Scale.

Key concepts

Mineral Hardness

The concept of mineral hardness is crucial in geology. It is determined using the Mohs Hardness Scale, which ranks minerals based on their ability to scratch each other. Hardness is a fundamental property that helps geologists determine the material composition of rocks and minerals. The scale ranges from 1 (softest) to 10 (hardest). For instance, talc is at the very bottom with a value of 1, while diamond rules the roost at 10. By understanding where a mineral falls on this scale, it becomes easier to predict how the mineral will respond to wear and tear over time.

Hardness can also indicate how a mineral can be used, both technically and for household purposes. Minerals with a higher Mohs value are used in cutting tools and abrasives, due to their ability to withstand scratches.

Geology Education

Geology education is not just about rocks; it's about understanding Earth's processes. Learning about minerals, including their hardness, teaches us about the forces that shape our planet. Educators use tools like the Mohs Hardness Scale to help students identify and analyze different minerals.

Understanding these concepts lays the foundation for more advanced studies in earth science, such as plate tectonics and earth's history. Classroom exercises might include hands-on activities, where students test real mineral samples for hardness. This experiential learning helps solidify what students read in textbooks, making the subject both practical and engaging.

Identifying Minerals

Identifying minerals is like being a detective in the world of geology. Among the key properties used, mineral hardness is one of the most reliable. By using tools like the Mohs Hardness Scale, geologists can quickly ascertain what a mineral might be by performing simple scratch tests.

Here’s how it works:

• Try to scratch the mineral using common substances or other minerals.
• If a mineral can scratch another, it's harder than the one it's scratching.
• Using this information, you can narrow down possibilities of what the mineral could be.

This method is not foolproof alone, and usually is used in combination with other identification tests such as color, luster, and streak. However, it's a straightforward and efficient starting point for amateur and professional geologists alike.