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Formula: [Pb(H2O)5(SO4)][Zn9(OH)18]
Sulphate
Crystal System: Monoclinic
Specific gravity: 3.513 calculated for the empirical formula, 3.522 calculated for the ideal formula
Hardness: 2½
Colour: Colourless
Luminescence: Does not fluoresce under long wave or short wave UV
Solubility: Dissolves rapidly in room-temperature dilute hydrochloric acid
Environments
Siligiite is a new mineral, approved on 2023 and to date (January 2025) has been reported only from the type
locality.
Localities
The type locality, the Redmond Mine, Waterville Lake, Haywood County, North Carolina, USA, is a very small and
long-inactive lead-zinc mine. The highly
unusual secondary assemblage of
lead - zinc -
copper sulphates, thiosulphates and carbonates found here is particularly
noteworthy for yielding phases with structures containing rare, and in some cases novel, structural units based on
short Pb2+–O bonds.
The ore, consisting mainly of galena and
sphalerite with lesser
chalcopyrite, occurs in an epithermal vein system consisting of disconnected
sulphide-bearing quartz lenses near the contact between a
granite gneiss and
mica schist. The new minerals occur in
a localised unusual secondary mineral assemblage.
Siligiite occurs in vugs in massive galena -
sphalerite - chalcopyrite -
quartz in close association with
anglesite, bechererite,
cherokeeite,
cuprocherokeeite, elyite,
kennygayite, leadhillite and
muscovite.
Siligiite crystals are elogated and striated blades or flattened needles, up to about 1 mm long, occurring in
radiating clusters; the mineral is colourless with a vitreous to silky lustre
(CJMP 62.6.881-889).
Siligiite from the Redmond Mine - Image
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