## Data Analysis

Based on Real Data*

Make and Use a Table

What information should you include in a mineral identification chart?

 Mineral Identification Chart Mineral Color Streak Hardness Breakage Pattern copper red 3 hackly, fracture red or reddish brown 6 irregular fracture pale to golden yellow yellow colorless 7.5 conchoidal fracture gray, green or white two cleavage planes

Analysis

1. Copy the data table and use the Reference Handbook to complete the table.

2. Expand the table to include the names of the minerals, other properties, and uses.

Think Critically

3. Determine which of these minerals will scratch glass? Explain.

4. Identify which of these minerals might be present in both a painting and your desk.

5. Identify any other information you could include in the table.

*Data obtained from: Klein, C. 2002. The Manual of Mineral Science.

Texture Texture describes how a mineral feels to the touch. This, like luster, is subjective. Therefore, texture is often used in combination with other tests to identify a mineral. The texture of a mineral might be described as smooth, rough, ragged, greasy, or soapy. For example, fluorite, shown in Figure 4.11, has a smooth texture, while the texture of talc, shown in Figure 4.6, is greasy.

Density and specific gravity Sometimes, two minerals of the same size have different weights. Differences in weight are the result of differences in density, which is defined as mass per unit of volume. Density is expressed as follows.

In this equation, D = density, M = mass and V = volume. For example, pyrite, has a density of 5.2 g/cm3, and gold has a density of 19.3 g/cm3. If you had a sample of gold and a sample of pyrite of the same size, the gold would have greater weight because it is more dense.

Density reflects the atomic mass and structure of a mineral. Because density is not dependent on the size or shape of a mineral, it is a useful identification tool. Often, however, differences in density are too small to be distinguished by lifting different minerals. Thus, for accurate mineral identification, density must be measured. The most common measure of density used by geologists is specific gravity, which is the ratio of the mass of a substance to the mass of an equal volume of water at 4°C. For example, the specific gravity of pyrite is 5.2. The specific gravity of pure gold is 19.3.

Figure 4.11 Textures are interpreted differently by different people. The texture of this fluorite is usually described as smooth.

Section 4.1 Assessment

Section Summary

I A mineral is a naturally occurring, inorganic solid with a specific chemical composition and a definite crystalline structure.

I A crystal is a solid in which the atoms are arranged in repeating patterns.

I Minerals form from magma or from supersaturated solutions.

I Minerals can be identified based on their physical and chemical properties.

I The most reliable way to identify a mineral is by using a combination of several tests.

Understand Main Ideas

1. imanList two reasons why petroleum is not a mineral.

2. Define naturally occurring in terms of mineral formation.

3. Contrast the formation of minerals from magma and their formation from solution.

4. Differentiate between subjective and objective mineral properties.

Think Critically

5. Develop a plan to test the hardness of a sample of feldspar using the following items: glass slide, copper penny, and streak plate.

6. Predict the success of a lab test in which students plan to compare the streak colors of fluorite, quartz, and feldspar.

«BOX» Earth Science

7. Calculate the volume of a 5-g sample of pure gold.

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Self-Check Quiz glencoe.com

Self-Check Quiz glencoe.com

Section 4.2

Objectives

I Identify different groups of minerals.

I Illustrate the silica tetrahedron. I Discuss how minerals are used.

Review Vocabulary chemical bond: the force that holds two atoms together

New Vocabulary silicate tetrahedron ore gem