What Mineral Test Is Shown In This Photograph

What Mineral Test is Shown in This Photograph? A Comprehensive Guide to Identifying Minerals

Determining the identity of a mineral from just a photograph can be challenging, even for experienced geologists. Visual identification alone is often insufficient, relying heavily on color, luster, crystal habit, and potentially cleavage or fracture. However, a photograph showing a specific test performed on a mineral drastically narrows down the possibilities and often provides definitive identification. This article will explore various mineral tests commonly photographed and will guide you through the process of identifying the test and subsequently, the mineral in question. Providing a photograph is crucial for accurate analysis.

Understanding Common Mineral Tests

Several tests help geologists and mineral enthusiasts identify minerals. These tests exploit the unique physical and chemical properties of different minerals:

1. Streak Test

• Description: This involves scratching the mineral across an unglazed porcelain plate (streak plate). The color of the powder left behind is the mineral's streak. This is particularly useful because mineral color can be deceiving due to impurities, whereas the streak tends to be more consistent.
• Photographic Identification: Look for a streak plate with a colored residue. The photo should clearly show the mineral sample and the resulting streak. The color and intensity of the streak are key pieces of information.
• Example Minerals: Hematite (red-brown streak), Pyrite (black-greenish streak), Galena (lead-grey streak)

2. Hardness Test (Mohs Hardness Scale)

• Description: This involves scratching the mineral with materials of known hardness using the Mohs Hardness Scale (1-10, with 10 being the hardest – diamond). By seeing what scratches the unknown mineral and what it scratches, its approximate hardness can be determined.
• Photographic Identification: Look for images showing the mineral being scratched by a known material (e.g., a fingernail, copper penny, glass, steel knife). The presence of scratches or lack thereof provides the hardness information.
• Example Minerals: Talc (Hardness 1), Gypsum (Hardness 2), Quartz (Hardness 7), Diamond (Hardness 10)

3. Acid Test (Hydrochloric Acid Reaction)

• Description: This involves applying dilute hydrochloric acid (HCl) to the mineral. Certain minerals, particularly carbonates, will effervesce (fizz) due to the release of carbon dioxide gas.
• Photographic Identification: Look for evidence of bubbling or fizzing when acid is applied. The intensity and speed of the reaction are important observations.
• Example Minerals: Calcite (vigorous reaction), Dolomite (slow reaction), Quartz (no reaction)

4. Magnetism Test

• Description: This test involves using a magnet to check if the mineral is magnetic. Some minerals, like magnetite, are strongly attracted to a magnet.
• Photographic Identification: Look for a magnet in proximity to the mineral sample. If the mineral is attracted, it will be visibly drawn towards the magnet.
• Example Minerals: Magnetite (strongly magnetic), Pyrite (weakly magnetic), most other minerals (non-magnetic)

5. Luster Observation

• Description: This isn't a test in the same way as the others, but it's a crucial visual observation. Luster refers to the way a mineral reflects light. Descriptions include metallic, vitreous (glassy), pearly, resinous, etc.
• Photographic Identification: The photo should clearly show the surface of the mineral and how it reflects light. Consider the lighting conditions in the photograph to ensure an accurate assessment.
• Example Minerals: Galena (metallic), Quartz (vitreous), Talc (pearly)

6. Cleavage and Fracture Observation

• Description: This involves observing how the mineral breaks. Cleavage refers to the tendency of a mineral to break along flat planes, while fracture is an irregular break. The type of cleavage (perfect, good, poor) and the direction of cleavage are important.
• Photographic Identification: The photo needs to clearly show the broken surface of the mineral. Examine the angles of the broken surfaces to determine cleavage type. If the fracture is irregular, note its description (e.g., conchoidal, splintery).
• Example Minerals: Mica (perfect basal cleavage), Halite (perfect cubic cleavage), Quartz (conchoidal fracture)

7. Specific Gravity Test

• Description: This determines the density of a mineral relative to water. It involves weighing the mineral in air and then submerged in water.
• Photographic Identification: A photo showing a balance scale used for specific gravity testing might be shown. However, specific gravity is typically not visually evident from a single photograph of the mineral alone. The calculation requires measurements.

8. Fluorescence Test

• Description: Some minerals exhibit fluorescence under ultraviolet (UV) light. This means they absorb UV light and re-emit it as visible light of a different color.
• Photographic Identification: The photograph would show the mineral under UV light, exhibiting a visible glow or change in color. The color of the fluorescence is a key diagnostic feature.
• Example Minerals: Fluorite (various colors), Calcite (fluoresces in various colors)

Analyzing the Photograph: A Step-by-Step Approach

To effectively identify the mineral test shown in a photograph, follow these steps:

1. Identify the Test: Carefully examine the photograph. Is there a streak plate present? A magnet? Hydrochloric acid being applied? This will give you the primary test being performed.

2. Observe the Results: Once the test is identified, observe the results. What color is the streak? Is there fizzing? Is the mineral attracted to the magnet? These observations are crucial.

3. Consider Additional Visual Cues: Pay close attention to the mineral's color, luster, crystal habit (shape), cleavage, and fracture. These characteristics, combined with the test results, provide a more complete picture.

4. Eliminate Possibilities: Based on your observations, eliminate minerals that wouldn't produce those results. For example, if the streak is red-brown, you can likely eliminate minerals known for their non-red streaks.

5. Consult Mineral Reference Materials: Use a mineral identification guide, handbook, or online database to compare your findings to known mineral properties. Cross-referencing your observations with the known properties of various minerals will help you narrow down the possibilities.

Example Scenarios and Photographic Interpretations

Let's consider a few hypothetical scenarios and how the photographic evidence would guide the identification:

Scenario 1: The photograph shows a white mineral sample being scratched easily by a fingernail. The mineral is showing a pearly luster. This indicates a low hardness (less than 2.5) and a pearly luster. This points towards a mineral like Gypsum or Talc.

Scenario 2: The photograph shows a dark gray mineral sample on a streak plate. A gray-black streak is visible. The mineral has a metallic luster. Hydrochloric acid is applied, and no reaction is observed. The mineral is strongly attracted to a magnet. This is indicative of Magnetite.

Scenario 3: The photograph displays a mineral sample reacting vigorously with dilute hydrochloric acid, showing a large amount of fizzing. The mineral is white-clear. This reaction strongly suggests a carbonate mineral, likely Calcite or Aragonite. Further observation of crystal structure (e.g., rhombohedral for Calcite) is needed to pinpoint the specific mineral.

Scenario 4: The photograph depicts a mineral with a distinct conchoidal fracture pattern. The mineral is hard (resistant to scratching with a steel knife), and has a glassy luster. The lack of reaction to acid, and its hardness eliminate numerous options. This points toward Quartz.

Conclusion: Combining Photographic Evidence with Other Data

While a photograph can provide valuable clues for mineral identification, it’s crucial to remember that it represents only a snapshot of the mineral's properties. Combining visual evidence from a photograph with additional tests and observations is critical for accurate and reliable identification. Remember to always prioritize safety when performing mineral tests, especially when using acids. Accurate mineral identification often requires a combination of visual observation, chemical tests, and the utilization of various mineral guides and identification keys.