- Chemistry: CaBePO4(F, OH), Calcium Beryllium
Phosphate Fluoride Hydroxide.
- Class: Phosphates
- Uses: As a very minor ore of beryllium and phosphorus and as mineral
Herderite is an attractive and except in some mines in New England,
a rather scarce phosphate mineral. It forms good crystals and can have
a nice yellow or light blue color. Its twinned
crystals are its most note-worthy form although its simple prismatic crystals
can have quite complex and interesting terminations. The twinning can produce
some very non-monoclinic looking crystals that could easily confuse identification.
Orthorhombic and nearly hexagonal twins are possible. A "fishtail"
twin has also been seen from deposits in Brazil. To top-off this mineral,
some specimens are fluorescent. A deep blue color can sometimes be seen
under longwave ultraviolet light. Herderite, with its beryllium chemistry,
possible fluorescence and both attractive and interesting crystal forms,
is certainly a nice addition to anybody's collection.
- Color is colorless, white, yellowish or pale green to blue-green.
- Luster is vitreous.
- Transparency: Specimens are transparent to translucent.
- Crystal System is monoclinic; 2/m
- Crystal Habits include prismatic crystals with a complex, but
over all domal termination. The prism faces may be rounded and etched.
is common forming cyclic twins that have a malformed hexagonal tabular
crystal. The "malformation" usually results in a crystal that
looks more orthorhombic than hexagonal and are easily confused with crystals
Other types of twinning can form "fishtail" twins similar
famous twins. Also found in nodules, fibrous aggregates, radiating clusters
and small grains.
- Cleavage is indistinct in two directions (prismatic).
- Fracture is subconchoidal.
- Hardness is variable from 5 - 5.5
- Specific Gravity is approximately 2.9 - 3.0 (average)
- Streak is white.
- Other Characteristics: Thermoluminescent, meaning it may glow
with a weak blue light upon extreme heating (but this test may damage the
specimen). Also sometimes fluorescent, showing deep blue in longwave ultraviolet
- Associated Minerals include those minerals common to phosphatic
- Notable Occurrences include Golconda Mine, Minas Gerais, Brazil;
several locations in Germany and Mursinsk, Russia. It the United States
there are several locations that produce plentiful supplies of good crystals
such as Newry, Stoneham and Topsham, Maine; Fletcher Mine, Alexandria,
New Hampshire and San Diego County, California.
- Best Field Indicators are crystal habit, color, fluorescence
if seen, hardness and localities.