Lollingite, or as it is alternatively spelled loellingite, is an uncommon
mineral, but is found with other arsenides and thus it is included with
them when mined for arsenic.
It is often associated with
FeAsS, and this
is unfortunate as it is difficult to distinguish between the two.
Their crystal forms, color, luster, streak and fracture are all very similar.
Lollingite is at least somewhat softer and denser.
Lollingite's composition is never exactly FeAs2, because it usually contains significant percentages of cobalt and nickel and sometimes sulfur.
Lollingite gives its name to a group of minerals
of which the mineral lollingite is one of the more common members. Members
of the Lollingite Group have a simple
formula, namely: AX2.
Where the metal ion, A, is either cobalt,
nickel and/or iron and the X can be
either arsenic and/or antimony with some members having some sulfur.
All members of the group have lollingite's basic structure.
They are all
orthorhombic in symmetry
and are very uncommon to rare in occurrence.
Some classification schemes place Lollingite Group members in the
These are the members of the Lollingite Group:
Costilbite(Cobalt Antimonide Sulfide)
Lollingite (Iron Arsenide)
(Cobalt Iron Arsenide)
Seinajokite(Iron Nickel Antimonide Arsenide)
Color is silver white to gray (tarnishes to a darker color).
Luster is metallic.
Transparency: Crystals are opaque.
Crystal System is Orthorhombic; 2/m 2/m 2/m
Crystal Habits include prismatic to stubby crystals with a chisel-like
domal termination. A crystal's cross-section will be diamond-shaped with
rounded oblique angles. Elongated wedge shaped crystals are seen when the
domal termination becomes dominant. Also compact, massive and disseminated
in veins fillings.
Twins are seen as star shaped trillings.
Cleavage is indistinct (basal).
Hardness is 5 - 5.5
Specific Gravity is approximately 7.1 - 7.5 (well above average
for metallic minerals)
Streak is a gray black.
Other Characteristics: Crystals are commonly striated lengthwise.
Associated Minerals include
Notable Occurrences include Lolling (hence the name), Huttenburg,
Carinthia, Austria; Harz, Germany;
Franklin, New Jersey; Cobalt, Connecticut;
Gunnison Co., Colorado; Alexander Co., North Carolina and
Ontario, Canada; Norway; Sweden; Finland; Czech Republic; Poland and Brazil.
Best Field Indicators are crystal habits, color, associations, streak,
hardness, striations and density.