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Formula: Mg2Fe3+O2(BO3)
Anhydrous borate,
ludwigite group, forms a series with
vonsenite
Crystal System: Orthorhombic
Specific gravity: 3.80 measured, 3.78 calculated
Hardness: 5
Streak: Greenish black
Colour: Dark green to black
Solubility: Slowly soluble in acids
Common impurities:Al
Environments
Ludwigite is a high-temperature borate typically formed in magnesian iron skarn
and contact metamorphic deposits (Mindat, Webmin, HOM, Dana).
Associated minerals include magnetite, forsterite,
clinohumite, vonsenite and
szaibelyite
(HOM). Ludwigite alters to limonite
(Mindat).
Localities
At Potrero Chico, Hidalgo, Nuevo Leon, Mexico, exposures of locally dolomitised,
magnesium-bearing limestone occur. The strata were uplifted
evaporites. Ludwigite, has been recovered from several
gypsum samples
(R&M 91-4.369).
At Sapat Gali, Naran, Kaghan Valley, Mansehra District, Khyber Pakhtunkhwa Province, Pakistan, black, acicular
inclusions of ludwigite in forsterite have been identified
(MinRec 51.6.785-801).
The type locality is Ocna de Fier, Ocna de Fier-Dognecea District, Banat Mountains, Caraş-Severin, Romania.
At Crestwood, California, USA, ludwigite occurs in limestone
(AM 46.335-339).
At Colorado Gulch, Lewis and Clark County, Montana, USA, ludwigite occurs abundantly 10 miles west of Helena. The prospect openings are in
dolomitised marble and
limestone a few yards from the contact of the Boulder batholith, which here consists of
sub-porphyritic quartz monzonite. Large
quantities of ludwigite are exposed. Ludwigite, intimately mingled with magnetite and a
minor amount of forsterite, was found to occur at the Redemption iron mine in the
contact zone of the Philipsburg batholith, about 50 miles southwest of the Colorado Gulch locality
(AM 27.824-825).
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