Round 1 Match 13
Proustite is a stunningly deep red sulfide mineral that entices with its translucent ruby red crystals. Proustite was historically an important source of silver and also contains arsenic in its structure. Proustite reminds us that not all sulfides are silver, grey or black but can form colourful crystals, too! Despite its softness, it can be faceted into a gemstone that superficially looks like ruby but without the abrasive power of corundum.
Titanite is an enigmatic mineral that can form in both igneous and metamorphic environments. It's hard enough to turn up in some sedimentary environments too! Titanite's main claim to fame is as an indicator mineral for everything from formation temperature, pressure and chronology. Titanite typically forms wedge-shaped crystals, from where its common alternate name sphene is derived - but the name titanite was recorded first.
Which shall it be: deep red sulfide proustite, or important indicator mineral titanite?
Prousite from Chile and Titanite from Brazil. Image credit: Smithsonian Institute
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