Question

Which mineral will scratch feldspar but not topaz? A. quartz C. apatite B. calcite D. diamond

Short answer

Quartz can scratch feldspar but not topaz.

Step-by-step solution

Understanding Mohs Hardness Scale

To identify which mineral can scratch another, understand that the Mohs hardness scale ranks minerals based on their ability to scratch each other. Feldspar is around 6, and topaz is around 8 on this scale.

Comparing Minerals Against Feldspar

We need a mineral harder than feldspar (hardness of 6) to scratch it. Check the hardness of options: Quartz (7), Apatite (5), Calcite (3), Diamond (10). Quartz at 7 can scratch feldspar.

Ensuring the Mineral Does Not Scratch Topaz

Topaz has a hardness of 8. Therefore, select a mineral with a hardness less than 8, to ensure it cannot scratch topaz. Quartz has a hardness of 7, which means it won't scratch topaz.

Checking All Conditions

The mineral must scratch feldspar but not topaz. Quartz is the mineral that satisfies both these conditions based on its hardness of 7.

Key concepts

Mineral Hardness

The Mohs Hardness Scale is a tool used to rank minerals by their ability to scratch one another. It assigns a numerical value to the hardness of a mineral, with 1 being the softest and 10 the hardest. This scale helps in quickly comparing the mineral's resistance to scratching.
Friedrich Mohs created this scale, and it's still widely used today because of its simplicity and effectiveness.

• The scale begins with the softest mineral, talc, rated as 1.
• Diamond is rated as 10, being the hardest natural material.

Understanding this scale can help in determining which minerals can scratch or be scratched by others.

Mineral Comparison

When comparing minerals, it is crucial to know their respective hardness levels on the Mohs scale. This knowledge determines which materials can scratch or be scratched by others.
Consider a mineral's hardness when predicting its durability and wear resistance for practical applications.

• If Mineral A has a higher hardness than Mineral B, it can potentially scratch it.
• If the hardness numbers are equal, neither can scratch the other.

This comparison is essential in fields like geology and jewelry making.

Scratch Test

The scratch test is a straightforward method to determine the hardness of a mineral. By scratching one mineral against another, you can judge which is harder.
This practical test is beneficial for geologists and collectors to quickly assess mineral properties in the field.

• If a mineral leaves a scratch, it is harder than the material being scratched.
• If no scratch is left, the mineral is softer or of similar hardness as the tested material.

Always clean and inspect minerals closely for accurate results.

Feldspar

Feldspar is one of the most common minerals found in the Earth's crust. It ranks 6 on the Mohs Hardness Scale, making it moderately hard.
This mineral is a significant component of many types of rocks, including granite and basalt.

• Feldspar's hardness means it can be scratched by any mineral with a higher rating than 6.
• It plays a crucial role in forming soils as it weathers over time.

Feldspar's unique properties make it an interesting subject of study in geology.

Quartz

Quartz is a well-known mineral due to its hardness of 7 on the Mohs scale. This makes it harder than feldspar but softer than topaz.
Quartz is abundantly present in the Earth's crust and is used widely in various industries.

• Its hardness means quartz can scratch minerals like feldspar, rated lower on the scale.
• However, quartz cannot scratch harder minerals like topaz, which is rated 8.

Quartz's durability and versatility make it an economic and scientific resource.

Topaz

Topaz is a striking and tough mineral with a hardness of 8 on the Mohs scale. It can scratch many minerals but not those rated higher, like diamond.
Known for its clarity and diverse colors, topaz is often utilized in jewelry.

• Topaz's high hardness contributes to its lasting polish and scratch resistance.
• It will not be scratched by quartz, which makes it a practical choice for wearables.

Topaz's resilience and beauty make it a favored gemstone among jewelers.