PSILOMELANE

( Fr- psilomélane; Ger- Psilomelan; Nor- psilomelan; Rus- )

PSILOMELANE ("may be used for hard unidentified [as to species] Mn oxides" per CNMMN
of IMA even though name has been discredited so far as application to any
mineral species)

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)

DESCRIPTION: As noted in the subheading of this entry, psilomelane is widely used as a waste-basket term for masses made up largely or wholly of hard, massive manganese oxides not specifically identified -- See also paragraph three under the REMARKS subheading.
    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."

OTHER NAMES:

Black hematite - an appalling/bizarre(?!) misnomer, that is apparently based on the fact that botryoidal psilomelane roughly resembles hematite ("kidney ore") but has a black streak (color of its powder) whereas hematite has a red streak.
Drusy psilomelane - name sometimes given to psilomelane coated with minute projecting colorless quartz crystals.
Psilomelane chalcedony - name sometimes given chalcedony with black bands, the blackness of which are due to the presence of Mn- oxide ["psilomelane"], from Mexico.

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.

Although I suspect some of the "drusy psilomelane" on the market has been titanium coated, to date, I have been unable to verify this possibility.

The nomenclature for the manganese oxides (plus or minus diverse amounts of H₂O) has gone through several stages. The following is NOT a review; rather it is given so readers will know the current status of some of the names they may encounter in descriptions that might be of interest to them -- be it while searching for rough material, fashioning items from it, or marketing items made from it: Psilomelane, once considered to be a mineral species, and currently rather widely applied to most relatively hard, massive gray to black manganese oxides used as gemrocks, is considered to be an historical remnant by professional mineralogists. The closest approach to an accepted name:composition match for much of the material once called psilomelane is the mineral species romanèchite; this "match" is based on the fact that psilomelane was frequently characterized as containing barium, and romanechite has the composition (Ba,H₂O)₂(Mn⁺², Mn⁺³)₅O₁₀. Yet another use of the term psilomelane, which is still in vogue in some quarters, was/is as a sack term to include massive masses of one or more of the following minderals: coronadite (PbMn₈O₁₆), cryptomelane (KMn₈O₁₆), hollandite (Ba,K,Ca,Sr)(Mn,Ti,Fe)₈O₁₆, manjiroite (Na,K)Mn₈O_16·nH₂O, and todorokite (Na,Ca,K,Ba,Sr)(Mn,Mg,Al)₆O₁₂·3-4H₂O. In addition, however, at least some manganese-rich materials called psilomelane contain other minerals -- e.g., pyrolusite (MnO₂) and the so-called massive manganese oxides often referred to as wad.

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 black dendritic inclusions. The latter misuse, fortunately more-or-less restricted to the marketplace, is apparently based on the fact that many black dendrites have been identified as Mn-oxide(s). And, to confound the confusion, the nabisco term psilodendrites (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 specimens.(www-2.cs.cmu.edu)

SIMULANT: 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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