can form as a thin coating when sphalerite-bearing rock is
exposed to water for many years.
The specimen above, found on the Buckwheat Dump, consists of a white crust of hydrozincite on a piece of dolomite. There is much pyrite and sphalerite in the rock as well.
Specimen is about 3 inches x 2 1/4 inches.
Right: The hydrozincite glows bright blue when exposed to
short-wave ultraviolet (SW UV).
At least some of the hydrozincite from Franklin and Sterling Hill formed after the overburden rock was cast on the dumps. Sparsely-covered and poorly-fluorescent specimens are common, but good ones are fairly hard to find. Unlike some of the other fluorescent minerals which have a "look" to them in daylight, it's impossible to tell without a short-wave lamp whether a hydrozincite is going to be any good..
|Above: Hydrozincite (FL Blue, SW) and
Calcite (FL Red, SW) from
Sterling Hill. The hydrozincite from this locality typically
forms as an alteration product of zincite,
unlike the material from Franklin which is usually a result of
sphalerite weathering. In other words, hydrozincite can form from
at least two different zinc minerals.
Just as at Franklin, it's usually necessary to sort through a great many poorly-fluorescing specimens before finding a hydrozincite of decent brightness. Sometimes the Sterling Hill material is phosphorescent after SW exposure, suggesting it's mixed with aragonite.
The specimen above is one of the nicer hydrozincites I've found at Sterling Hill, at least of those that occur on the heavy zincite-franklinite ore assemblage. Size is about 3 1/2 inches across maximum dimension.
Incidentally, some of the best New Jersey hydrozincite specimens ever found were recovered from the bottom of Lake Hopatcong, a result of Franklin-Sterling Hill ore pieces that had fallen off a barge many years before! Robert Jones's Nature's Hidden Rainbows mentions this story in a little more detail, if I remember correctly.