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What is the exact difference between a crystal and a mineral?

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  • $\begingroup$ Welcome. How are they formed is too broad sorry. $\endgroup$
    – user20559
    Jan 16 at 12:53
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    $\begingroup$ Almost all minerals are crystals. Not all crystals are minerals. Quartz is both. Sugar is a crystal, but not a mineral. $\endgroup$
    – Gimelist
    Jan 16 at 22:42

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A crystal,

is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions.

Microscopically, a single crystal has atoms in a near-perfect periodic arrangement; a polycrystal is composed of many microscopic crystals (called "crystallites" or "grains"); and an amorphous solid (such as glass) has no periodic arrangement even microscopically.

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Examples of crystals include diamond (C), table salt (NaCl), snow and ice (H2O) and chalcopyrite (CuFeS2).

Minerals however,

a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.

The international Mineralogical Association requirements for classification minerals are:

  1. It must be a naturally occurring substance formed by natural geological processes, on Earth or other extraterrestrial bodies.
  2. It must be a solid substance in its natural occurrence. A major exception to this rule is native mercury.
  3. It must have a well-defined crystallographic structure; or, more generally, an ordered atomic arrangement.
  4. It must have a fairly well defined chemical composition. However, certain crystalline substances with a fixed structure but variable composition may be considered single mineral species.

Consequently, snow and ice are crystals but they are not minerals.

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  • $\begingroup$ Ice is actually a mineral, approved by the IMA: mindat.org/min-2001.html although somewhat polarising because a lot of mineralogists don't consider it as a "real" mineral 😂 $\endgroup$
    – Gimelist
    Jan 17 at 23:04
  • $\begingroup$ Every academic mineralogist/petrologist I've known considers ice a mineral; especially given it's importance in planetary geology. $\endgroup$ Jan 23 at 0:13

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