( Fr- psilomélane; Ger- Psilomelan; Nor- psilomelan; Rus- )
be used for hard
unidentified [as to species] Mn oxides" per
of IMA even though name has been discredited so far as application to any
Psilomelane. Labeled as "Cryptomelane, " this nodule (greatest dimension ~35 cm) is from now abandoned Crimora mine, Augusta County, Virginia. Michaels Museum collection (VPI&SU, Blacksburg, Virgina). (photo by Mark Fortney)
noted in the subheading of this entry, psilomelane is widely used as a
made up largely or wholly of hard, massive manganese oxides not
identified -- See also paragraph three under the REMARKS
Color - black to silvery black.
H. 5 - 6½ -- Possible Mn-mineral components noted in the REMARKS have recorded values ranging from 2 to 6½.
S.G. 4.3-4.8 -- Possible Mn-mineral components noted in the REMARKS have recorded values ranging from 4.3 to 5.44.
Light transmission - opaque
Luster - dull, velvety (on fresh fracture surfaces), submetallic
Miscellany - botryoidal masses or crusts are common; brownish black streak; soluble in concentrated HCl (hydrochloric acid), releasing chlorine gas with its distinctive ordor; some psilomelane is said to feel like velvet -- although some fresh surfaces have a velvety appearance, I have not encountered any that felt like velvet.
Because of the preceding statement, Ashley Bradford (p.c. -- email, 1 Nov.2011 --) directed my attention to photographs of a specimen from Socorro County, New Mexico that exhibit a surface that has such a "feel." She indicates it feels "very much like a chenille sweater. Not quite as soft as Cashmere, but that's possibly just due to how short the "pile" is and the fact that there's a very hard surface [beneath it]." I find this especially interesting because the Greek ψιλόϛ from which the Psilo part of the name originally given to this "mineral' means smooth or bald, whereas the presence of a "pile" atop the typically smooth surfaces of this "mineral" are apparently required to account for the velvetlike "feel."
USES: So far as a gemrock, uses similar to those for hematite and with the same limitations, which relate to its relatively high specific gravity. "Drusy psilomelane," in particular, has been used for brooches and pendants (especially wire-wrapped ones); spheres.
OCCURRENCES: As a weathering product, typically as botryoidal masses, in unconsolidated deposits -- e.g., residual clays.
NOTEWORTHY LOCALITIES: Schneeberg (Saxony), Germany; near Thumb Butte in the Palo Verde Mountains, Imperial County and at the Arlington mine, northwest of Blythe, Riverside County, California; the Soccoro Valley, New Mexico; the abandoned Crimora mine, Augusta County, Virginia.REMARKS: Psilomelane comes from the Greek ψιλόϛ (smooth) and μέλαν (black). The first use of this term, according to OED notes that ".The name psilomelane...is formed in allusion to the black colour and smooth hematitic shapes of the mineral." The hematitic shapes apparently refer to the common botryoidal (shaped like a bunch of grapes) hematite -- see Figure C in HEMATITE entry as well as illustration in this entry.
To confuse the issue further, in
the “lapidary world,” the term psilomelane is
frequently misapplied to psilomelane
chalcedony and even to moss agate that includes relatively abundant
dendritic inclusions. The latter misuse, fortunately more-or-less
restricted to the
is apparently based on the fact that many black dendrites have been
as Mn-oxide(s). And, to confound the confusion, the nabisco term
(apparently meant to suggest that the dendrites consisting of
psilomelane) is also referred to
dendrite-bearing/coated rocks such as quartzites that have been
fashioned into jewelry or even exhibited as display
Especially in the past, psilomelane
has been used as a substitute for hematite
in jewelry. - [Inferior specific
gravity. Powder is black.].
REFERENCES: No general reference. Milch,1994; Potter and Rossmann,1979 &1979A.
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R. V. Dietrich © 2011
Revised: November 3, 2011
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