1) Trigonal mineral 
Olgite is a rare blue-green colored phosphate mineral series that forms microscopic prismatic crystals that are trigonal in structure. Its chemical formula is Na(Sr,Ba)PO4. Olgite was discredited as a mineral name in 2008 by the International Mineralogical Association and is now the series name for bario-olgite and strontio-olgite (hypothetical mi...