Minerals in space group 198

Gersdorffite or Nickel glance (trivial name) is a nickel arsenic sulfide mineral with formula NiAsS. It crystallizes in the isometric system showing diploidal symmetry. It occurs as euhedral to massive opaque, metallic grey-black to silver white forms. Gersdorffite belongs to a solid solution series with cobaltite, CoAsS. Antimony freely substitutes also leading to ullmannite, NiSbS. It has a Mohs hardness of 5.5 and a specific gravity of 5.9 to 6.33.

Ullmannite or Nickel glance (trivial name) is a nickel antimony sulfide mineral with formula: NiSbS. Considerable substitution occurs with cobalt and iron in the nickel site along with bismuth and arsenic in the antimony site. A solid solution series exists with the high cobalt willyamite.

Langbeinite is a potassium magnesium sulfate mineral with the chemical formula K2Mg2(SO4)3. Langbeinite crystallizes in the isometric-tetartoidal (cubic) system as transparent colorless or white with pale tints of yellow to green and violet crystalline masses. It has a vitreous luster. The Mohs hardness is 3.5 to 4 and the specific gravity is 2.83. The crystals are piezoelectric.

Brownleeite is a silicide mineral with chemical formula MnSi. It was discovered by researchers of the Johnson Space Center in Houston in April 2003 while analyzing the Pi Puppid particle shower of the comet 26P/Grigg-Skjellerup. The only other known natural manganese silicide is mavlyanovite, Mn5Si3.

Efremovite is a rare ammonium sulfate mineral with the chemical formula: (NH4)2Mg2(SO4)3. It is a white to gray cubic mineral. This anhydrous sulfate occurs as constituent in sulfate crusts of burning coal dumps. It is hygroscopic and when exposed to humid air it slowly converts to the hydrate form, boussingaultite.

Naquite is a mineral of iron monosilicide, FeSi. It was discovered in the 1960s in Donetsk Oblast in Soviet Union, and named fersilicite, but was not approved by the International Mineralogical Association. It was later rediscovered in the Nagqu area of Tibet and given the name naquite. Naquite occurs together with other rare iron silicide minerals, xifengite (Fe5Si3) and linzhiite (FeSi2).