Hornblende is a dark, opaque mineral that stands out in rocks due to its distinctive color and crystal forms. It is a common component in many igneous and metamorphic rocks, making its appearance a key identifier for geologists and rock enthusiasts.
Visual Characteristics of Hornblende
When examining hornblende in a rock, its visual features are the primary indicators of its presence.
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Color: Hornblende is typically opaque and displays a range of dark colors, including:
- Green (from opaque green to dark green)
- Brown
- Black
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Crystal Form and Habit: The way hornblende crystals grow gives them a characteristic appearance:
- Prismatic to Bladed Crystals: It commonly forms long, slender, or flattened crystals within the rock matrix.
- Diamond-Shaped Cross-Section: When viewed from the end of a crystal, its cross-section often appears distinctly diamond-shaped.
- Irregular Grains: Hornblende can also be present as less defined, irregular, or blocky grains.
- Fibrous Masses: In some instances, it may form tangled, fiber-like aggregates.
Key Physical Properties
Beyond its visual appearance, hornblende possesses specific physical properties that are useful for its identification and characterization:
| Property | Description |
|---|---|
| Hardness | 5–6 on the Mohs scale of mineral hardness |
| Specific Gravity | 3.0 to 3.6 |
These properties, combined with its distinct dark coloration and crystal shapes, make hornblende a readily identifiable mineral in various rock types, such as granites, diorites, and amphibolites. For more detailed information about hornblende and other minerals, you can explore resources like Geology.com's mineral profiles.
