| 21. | It has low hygroscopicity, and its Mohs hardness is 4.5.
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| 22. | It has a Mohs hardness of 3 to 4 and its cleavage is perfect.
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| 23. | For comparison, common glass has a Mohs hardness of 5.5.
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| 24. | Its structure is monoclinic with a Mohs hardness of 3.5 and lacks regular cleavage.
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| 25. | The Mohs hardness is 5.5, and the specific gravity 2.47.
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| 26. | It has a Mohs hardness of about 6.5 to 7.0 depending on the composition.
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| 27. | It has a Mohs hardness of 5 and a specific gravity of 2.81 2.87.
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| 28. | It is soft with a Mohs hardness of 2 and a specific gravity of 3.
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| 29. | He refers to using one hard mineral to scratch another, presaging the Mohs hardness scale.
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| 30. | It has a Mohs hardness of 3, exhibits no cleavage and has a splintery fracture.
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