Troctolite

Troctolite is not a mineral but a rock belonging to the group of mafic plutonites.

Typically plutonites have a coarse-grained fabric, consisting almost exclusively of well crystallized minerals, most of them visible to the naked eye.
Essentially troctolite contains variable amounts of olivine and plagioclase feldspar (labradorite and bytownite) as well as minor amounts of pyroxene, biotite, hornblende, magnetite and others.

Trotolith troctolite forellenstein trout stone
Troctolite from Gloggnitz, Lower Austria

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Origin of name: from Greek τρώκτης (troktis), trout and λίθος (lithos), stone, thus trout stone in allusion to its speckled appearance

Localities: worldwide at least 30 localities are known, e.g. in the USA, China, Pakistan, South Africa and Tanzania. In Europe Troctolite was found in Albania, the UK, Germany, Poland and Austria

Worth knowing: troctolite was also found on the moon. Amongst samples collected by American astronaut geologist Harrison Schmitt during the Apollo 17 mission in 1972, there was a 5cm large troctolite. It was labelled "Lunar Sample 76535" and is described by Nasa as "without doubt the most interesting sample returned from the Moon!"