RHÖNITE
RHÖNITE Rhönite – Ca4[Mg8Fe3+2Ti2]O4[Si6Al6O36] – is a fairly rare inosilicate, characteristic of alkaline rocks. It is not an ore. It is classified in the Sapphirine Supergroup, Rhönite Group, along with aenigmatite. It can form prismatic to tabular crystals several centimeters long. It also occurs in skeletal grains with well-developed crystal faces and as anhedral grains. […]
REALGAR
REALGAR Realgar – As4S4 – is a rarer sulfide. It has some importance as an As ore, along with arsenopyrite and orpiment. It normally occurs very pure. It is trimorph with alacránite and pararealgar. Sometimes it’s fluorescent. Macroscopically it can be confused with sarawaite and other red As-S minerals. As realgar is photosensitive, it changes […]
RANCIÉITE
RANCIÉITE Ranciéite – (Ca,Mn2+)0.2(Mn4+,Mn3+)O2·0.6H2O – is a rarer oxide, a minor component of Mn ores, with 75.34% MnO2. It is classified in the Birnessite Group, in the Ranciéite-Takanelite Series, the two being isostructural. Macroscopically it can be confused with todorokite, but X-ray diffractograms are diagnostic, somewhat variable depending on the degree of hydration. The literature […]
RHODOCHROSITE
RHODOCHROSITE Rhodochrosite – MnCO3 – is a rarer carbonate. It is a very secondary ore of Mn and has many uses as a decorative stone, fetching high prices in the collector and ornamental stone market, but it is not suitable for stoning. Once exposed to the atmosphere, it can develop a thin black surface film […]