Phenacite

noun

1. A natural beryllium silicate, Be₂SiO₄, occurring as vitreous crystals sometimes used as gems.
2. A rare mineral occurring in transparent rhombohedral crystals, colorless to wine-yellow, and having a vitreous luster.
3. A glassy colorless mineral occurring in rhombohedral crystals, sometimes used as a gem. It is a silicate of glucina, and receives its name from its deceptive similarity to quartz.
4. A clear <xref>glassy</xref> <xref>mineral</xref>, a <xref>silicate</xref> of <xref>glucina</xref>, occurring in <xref>rhombohedral</xref> <xref>crystals</xref> and sometimes used as a <xref>gem</xref>.