Anhydrous borate, ludwigite group, forms a series with vonsenite
Specific gravity: 3.6
Streak: Greenish black
Colour: Dark green to black
Solubility: Slowly soluble in acids
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
(HOM). Ludwigite alters to limonite
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).
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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