One level back to [Semi-metal oxides]. 2.2.3.3.3.2.1.2.2. [Rock crystal, opal, amethyst] Metal oxides] (aluminium oxide, corundum, iron oxide etc.) 22333213
One level back to [Semi-metal oxides]. 2.2.3.3.3.2.1.2.2. [Rock crystal, opal, amethyst]

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[Rock crystal, opal, amethyst]