Since glass is amorphous quartz and when you slow the cooling of something enough it will crystallize, couldn’t you melt $\ce{SiO2}$ (sand) and then very slowly cool it to cause spontaneous nucleation and form quartz crystals?

If so, then why hasn’t it been used before? It would seem to be a better method than flux because in flux you need many chemicals and a dissolving chemical or mix and it is a complicated and very long process to grow very small crystals throughout the whole mix. If you simply cooled a molten mixture slowly enough to cause complete crystallization, then the entire mix of molten crystal would need to form crystal because it all is cooling down.

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    $\begingroup$ About the second part of your question, both the α- and the β-phase of quartz have what we call an enantiomorphic space group. It forms spirals that can be 'enantiomers' to each other, which I guess also gives it its properties. For many applications you often need the pure enantiomer which will grow in a seed of the correct orientation under for example hydrothermal conditions. $\endgroup$ May 27, 2019 at 8:27
  • $\begingroup$ Melting and cooling will give you a bunch of crystals lumped together. Why would you want that? Then again, I've seen single crystals of quartz as big as a tabletop, and they were not made by melting. $\endgroup$ May 27, 2019 at 8:29
  • $\begingroup$ see eg ndk.com/catalog/AN-SQC_GG_e.pdf $\endgroup$
    – Buck Thorn
    May 27, 2019 at 8:47
  • $\begingroup$ In principle, maybe. But that isn't how big crystals are formed in nature. Most deposit from solutions not from melted pure silica. $\endgroup$
    – matt_black
    May 27, 2019 at 13:03
  • $\begingroup$ @NightWriter Your example post is about hydrothermal growth of a crystal. $\endgroup$
    – Buttonwood
    May 27, 2019 at 21:37


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