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Euhedral and anhedral
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<p>Euhedral and anhedral are terms used to describe opposite properties in the formation of <a href="/facts/Crystal/e2R2mk3E">crystals</a>. Euhedral (also known as idiomorphic or automorphic) crystals are those that are well-formed, with sharp, easily recognised <a href="/facts/Face_(geometry)/T2E6BTU4">faces</a>. The opposite is anhedral (also known as <i><a href="/facts/Xenomorph_(geology)/NvI7sWq0">xenomorphic</a></i> or <i>allotriomorphic</i>), which describes rock with a <a href="/facts/Rock_microstructure/rsR0CG11"> microstructure</a> composed of mineral grains that have no well-formed crystal faces or cross-section shape in <a href="/facts/Thin_section/FygaCHxS">thin section</a>. </p><p>Anhedral crystal growth occurs in a competitive environment with no free space for the formation of crystal faces. An intermediate texture with some crystal face-formation is termed subhedral (also known as <i>hypidiomorphic</i> or <i>hypautomorphic</i>). </p><p>Crystals that grow from cooling liquid <a href="/facts/Magma/hRotHju9">magma</a> typically do not form smooth faces or sharp crystal outlines. As magma cools, the crystals grow and eventually touch each other, preventing crystal faces from forming properly or at all. </p><p>When <a href="/facts/Snowflake/KUWqwqbP">snowflakes</a> crystallize, they do not touch each other. Thus, snowflakes form euhedral, six-sided <a href="/facts/Crystal_twinning/7xU6CKfR">twinned</a> crystals. In <a href="/facts/Rock_(geology)/FXCJkmop">rocks</a>, the presence of euhedral crystals may signify that they formed early in the crystallization of liquid magma or perhaps crystallized in a cavity or <a href="/facts/Vug/V9n4Gj8N">vug</a>, without <a href="/facts/Steric_hindrance/TnX5c8HG">steric hindrance</a>, or spatial restrictions, from other crystals. </p>