The optical clarity of of colorless sapphire stone and its unique refraction of light and strength for example, is not comparable to the clarity, etc. of amorphous/glass laminates.

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    $\begingroup$ I think military canopies are all acrylic or polycarbonate. They're tough and relatively easy to manufacture. $\endgroup$
    – atc_ceedee
    Jul 17 '21 at 17:34
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    $\begingroup$ If a combat plane has a windshield, it'll be of laminated armour glass, similar to the glass used in an armoured trucks. $\endgroup$
    – John K
    Jul 17 '21 at 18:28
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    $\begingroup$ Sapphire(which is basically aluminum oxide with impurities that give it a blue color) wouldn't be used for windows, since it doesn't occur in large enough pieces, and the impurities give it color. (Many other gemstones are also aluminum oxide, with different impurities. If it doesn't have the right impurities, it's not sapphire.) Fused aluminia (manufactured) is available, but I think fused quartz is more common. IIRC, the Space Shuttle's windows were made of it. $\endgroup$
    – jamesqf
    Jul 18 '21 at 4:22
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    $\begingroup$ @Jasen The iPhone uses Gorilla Glass for the screen. It only uses synthetic sapphire on its back camera lenses. $\endgroup$
    – Eric S
    Jul 18 '21 at 14:22
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    $\begingroup$ @Jasen: It's not "synthetic sapphire", whatever lies Apple's marketing division may tell. It's fused alumina. $\endgroup$
    – jamesqf
    Jul 18 '21 at 17:04

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