Schorl from Erongo, Namibia. Specimens and photo – J de Jongh
Crystal system:                        trigonal                         Hardness:         7
Density:                                    3.1 - 3.25                      Cleavage:         None
Streak:                                     white                            
Colour:                                       black, brownish black, bluish black
Occurrence:     Schorl is a common accessory mineral in granite pegmatites, tin-mineralized granites and in some metamorphic rocks.
Habitat:            Crystals are short to long prismatic, vertically striated, also acicular, rarely flattened as thin tablets. As single crystals or as radiating groups of crystals. Also massive, compact, columnar to fibrous.
Composition:   silicate      NaFe2+3Al6(BO3)3Si6O18(OH)4
    As the Mineral Discussion Group was focusing on the minerals from the Erongo Mountains in Namibia this past month, it is appropriate to discuss one of the minerals from this famous locality. Although not regarded as very sought after tourmaline specimens, a perfect schorl crystal always catches the eye. The reason for this is simple; it symbolizes perfection in nature, similar to a perfect pyrite, fluorite or garnet crystal. Please note that the correct pronunciation of this mineral name will improve with each pint consumed.
    The name “schorl” comes from the early German mining term ”schrul”, later “schurl” and “schril”, referring to the black stones that were rejected in the washing of gold and tin ores. This mineral was first mentioned by Ulrich von Calw in 1505.
    Schorl is the iron–rich member of the tourmaline group and the most common tourmaline. It forms distinctive jet-black crystals, but can also be found in deep red and deep mauve colours.
    World wide localities include USA, Canada, Mexico, England, Brazil, Greenland, Norway USSR, Afghanistan, Pakistan, Japan and Madagascar. Crystals measuring up to 5 m long were found at Arendal, Norway. Schorl is also found at various localities scattered all over Namibia and South Africa.
    Some crystals from the Erongo Mountain pegmatites are considered the finest in the world and have raised the status of this rather mundane mineral. Single, jet-black, prismatic crystals are known, up to 40 cm long, with mirror-like luster. There are various habitats, from crystals resembling garnets, radiating fans, multiple terminations, vermiform, dimpled terminations, table-like overgrowth, selective continued growth, and hollow crystals to crystals with triangular terminations which imitate the Mercedes Benz logo…..and the list goes on.
    They occur as single crystals or in clusters over 50 cm from edge to edge and as stunning specimens when they are associated with deep blue aquamarine, green fluorite and with white feldspar. Research suggests that some of these black crystals may not be schorl, but rather the very rare tourmaline foitite or even a new species of tourmaline altogether (best left to be identified by the gurus).
    Schorl may have parallel lines called striations running along or across the face of crystal. These are usually caused by two forms of the same crystal trying to grow at the same time.   JdJ