þolkíslungur (topaz)

There is no Icelandic term for "silicate" or "silicate mineral", although it is relatively easy to construct one.  The Orðaskrá um eðlisfræði og skyldar greinar mentions kísl for silica (SiO2, silicon dioxide).  Silicates are compounds with silica or oxidized silicon, so all we have to do is adding -ungur or
-ingur to kísl: kíslungur.  compounds: e.g. neosilicate = nýkíslungur.  The topaz is the hardest silicate mineral in nature.  Initially I thought of kóngakíslungur, harðkíslungur, but the best choice in my opinion is þolkíslungur.