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| a combination of hardness, toughness and stability |
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| the ability of a material to resist abrasion when a pointed fragment of another substance is drawn across it without sufficient pressure to develop cleavage or fracture |
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a non-linear scale based on ten minerals, numbered one to ten in increasing order of hardness
each mineral will scratch those of a lower number and can be scratched by those of a higher number |
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| hardness which differs with the direction of scratching; due to the structural arrangement of planes and directions of atomic bonding in certain crystal structures |
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| the ability of a material to resist the development of fracture and cleavage through the body of the material |
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| the random, non-directional breakage which occurs in most gemstones as a result of stress; stress can be due to internal or external forces such as a sudden temperature change or a sharp knock |
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| a broken surface with concentric, raised surface markings looking similar to the ridges on a seashell |
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| the uneven and often jagged surface that occurs when a material is fractured; this texture typically occurs in fractures through tough materials composed of intergrown fibrous cyrstals |
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| the ability, possessed by some crystalline gem materials, to split along certain well-defined crystal structure planes to leave more or less flat cleavage faces |
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| the ability of a material to resist physical or chemical alteration due to light, heat, or chemical attack |
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| cleavage that has developed a crack within a material but which has not yet caused teh material to break open |
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| a characteristically colored posder seen whan a material is scratched or drawn across an unglazed white porcelai plate to leave a 'streak' of powder |
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| a tendency for a crystal structure to split along planes of weakness resulting from lamellar twinning |
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