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Chemical Formulas:
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Pyroxene: The general formula for pyroxene minerals is \( \text{XY(Si, Al)}_2\text{O}_6 \), where \( \text{X} \) can be a divalent metal cation (like Mg, Fe, or Ca) and \( \text{Y} \) can be a trivalent cation (like Al or Cr). Specific pyroxene minerals, like augite, can have a more detailed chemical formula such as \( \text{(Ca, Na)(Mg, Fe, Al)(Si, Al)}_2\text{O}_6 \).
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Biotite: The chemical formula for biotite is generally expressed as \( \text{K(Mg, Fe)_3(AlSi}3\text{O}{10})(OH)_2 \). It can have variations depending on the specific chemical composition.
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Cleavage Classification and Degree:
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Pyroxene: Pyroxene typically has two directions of cleavage at approximately 90 degrees, classified as "perfect" cleavage because of its distinct and well-defined cleavage planes.
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Dioptase: Dioptase has perfect cleavage in one direction, but it's not as pronounced as in other minerals. The cleavage is classified as "good" in one direction.
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Biotite: Biotite exhibits perfect cleavage in one direction, and this is also classified as "perfect" because of the ease of separation along its cleavage planes.
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To summarize:
- Pyroxene: Perfect cleavage at approximately 90 degrees.
- Dioptase: Good cleavage in one direction.
- Biotite: Perfect cleavage in one direction.
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