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Crystal habit

Shape and size give rise to descriptive terms applied to the appearance, or habit of crystals.

The crystals of some minerals for example, form long needles, tapped or pointered at the ends. We say they have a acicular habit. Some, which are elongated, but not tapped, or come with a sharp point, are said prismatic. Other crystals are stubbier and ressemble a barrel, they are said to have a barrel-shapped habit. If crystal are long and flat, they are bladed. Very long and thin-hair like, they are called filiform.

Aggregates of crystal may adop forms that are specific of certains minerals. Hematite for example, is found often in colloform or reniform groupings. Other terms used are botryoidal, mammillary, and tuberose. Some minerals said foliated or micaceous, also tend to part along cleavages to form thin sheets. The ones that break in fibers are said to have fibrous habit, those that come apart as granules are said granular. A dendritic habit describes minerals whose crytals branch like trees, from a central trunk, usually in two directions. Feathery crytals are said plumose. Needlelike converging in many directions are said 'stellate or star-shapped.

The many terms used by mineralogists for habits are useful in discribing what specimens of a particular mineral often look like. Recognising numerous habits help a mineralogist to identify a large number of kwon mineral.



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