PYRRHOTITE with SPINEL and CALCITE (small cabinet)

Pyrrhotite, derived from the Greek word for "flame-colored," is an uncommon iron sulfide mineral represented by the formula Fe(1-x)S, where x ranges from 0 to 0.125. This mineral is a nonstoichiometric form of FeS, commonly referred to as troilite. Often called magnetic pyrite due to its color resemblance to pyrite, pyrrhotite exhibits weak magnetism that diminishes with increasing iron content, while troilite remains non-magnetic. Typically, pyrrhotite appears tabular with a brassy or bronze hue and a metallic sheen. It is commonly found in association with mafic igneous rocks such as norites and can form from the alteration of pyrite during metamorphic events.

Spinel is a mineral belonging to the magnesium/aluminium category within the broader spinel group, characterized by the chemical formula MgAl2O4 and forming in a cubic crystal system. The term "spinel" is derived from the Latin word "spinella," which means little thorn, reflecting the mineral's sharp crystal points.

Spinel exhibits isometric crystallization, with octahedral shapes being the most common, often appearing in twinned formations. While it lacks true cleavage, it displays octahedral parting and conchoidal fractures. With a hardness rating of 8 and a specific gravity ranging from 3.5 to 4.1, spinel can be found in a variety of appearances, from transparent to opaque, and possesses a vitreous to dull luster. Its color spectrum includes shades of red, lavender, blue, green, brown, black, and yellow, with chromium(III) being responsible for the red hues found in Burmese spinel.

Former collection: John Betts, Personally Collected in 1996, collection nr 11688 (comes with original tag)