LEUCOPHOENICITE

Leucophoenicite is a manganese silicate hydroxide mineral of the leucophoenicite group. Dunn (1985a) provided 27 modern analyses and made the following compositional observations:
1. Most leucophoenicites are highly calcic. Of the 27 analyses, 22 have Ca values in excess of 0.48 Ca per 3 Si. It should be emphasized, however, that this ratio is misleading; calcic material is much more common, as evidenced by unpublished data. No samples contained the very high (up to 14 wt. %) CaO values reported by Cook (1969) using XRF analysis. The abundance of samples with values of 0.5-0.7 Ca per 7 octahedral cations suggests that this is a somewhat "stable" calcium content for samples which form in calcic assemblages.
2. Zn is a constant constituent of Franklin material. It is present in all analyses of local leucophoenicite, including many not published here. It is relatively invariant, amounting to approximately 0.3 Zn per 3 Si. No Franklin leucophoenicite was found which contained the very high zinc content (up to 8 wt. % ZnO) reported by Cook (1969) using XRF analysis. Using material from other localities, Dunn et al. (1988) showed Zn to be non-essential to leucophoenicite.
3. Fluorine is essentially absent in leucophoenicite. Some samples may have traces of F, which are well within the error of the microprobe determinations.
Leucophoenicite was originally described from Franklin, New Jersey, by Penfield and Warren (1899). Subsequent studies of its morphology were published by Palache (1928, 1935) and Moore (1967), and optical absorption data were given by Keester and White (1966). The discovery of jerrygibbsite, a polymorph of Mn₉(SiO₄)₄(OH)₂, by Dunn et al. (1984d) led those authors to speculate that there might be additional members of the leucophoenicite family and that jerrygibbsite might be one of these.
Leucophoenicite originally was known only from the zinc deposit at Franklin, New Jersey; it has never been reported from Sterling Hill.
Leucophoenicite is structurally distinct from the humite-group minerals, with which it has strong compositional similarity and is sometimes associated. Brovkin and Nikishova (1975) showed the relation of the structures of Mg₅(BO₃)₃F and leucophoenicite. White and Hyde (1983a, 1983b), using TEM techniques, showed that leucophoenicite is a member of a family of crystal structures (including some borates and germanates) and supported Moore's (1970b) proposal of edge-sharing, half-occupied silicate tetrahedra. Yau and Peacor (1986) studied leucophoenicite-jerrygibbsite intergrowths using TEM methods and showed that the differences between the Mn-humites and leucophoenicites are due to unit-cell twinning. They also suggested that leucophoenicite-group minerals might form in the absence of fluorine. Kato (1988) suggested that Ca is not essential to the leucophoenicite structure, and he provided crystal-structure refinements of Ca-rich and Ca-poor leucophoenicites. The description of the crystal structure of ribbeite (Freed et al., 1993) provided additional descriptions of the features common to leucophoenicite-related minerals.
Leucophoenicite is commonly some shade of pink, but violet-red and brownish-red hues are known. It occurs as both massive material and as euhedral crystals. No morphological studies have been done since those of Palache (1935) and Moore (1967). The luster is vitreous; cleavage was reported by Penfield and Warren (1899) but was not observed by [Dunn]; and the density is 3.85 g/cm³. There is no discernible fluorescence in ultraviolet. Leucophoenicite is distinguished from hodgkinsonite by the perfect cleavage and lower indices of refraction of the latter. Leucophoenicite is best distinguished using X-ray methods.
Leucophoenicite is a moderately common mineral at Franklin, occurring in secondary veins and adjacent ore. Recrystallized material was common, especially in the Parker Mine, but leucophoenicite is not known from Sterling Hill. It occurs in veins and vuggy assemblages in association with a number of associated minerals, and it is found in calcium-rich primary ore, hydroxyl-bearing ore assemblages, and recrystallized aggregates. In vein assemblages, leucophoenicite crystallizes late, commonly contemporaneously with willemite, the most commonly associated mineral. Other associated species are calcite, andradite, sonolite, franklinite, zincite and vesuvianite.
Several hundred leucophoenicite samples were examined. The results of this comparison supported that leucophoenicite occurs in a great variety of assemblages, most of which contain calcite or Ca-bearing associated minerals such as andradite. Most of the preserved pink-colored material from Franklin is leucophoenicite and not jerrygibbsite. However, it is not clear whether this is due to selective retention of the more attractive bright-pink leucophoenicite by miners' casual collecting, or if this apparent predominance of leucophoenicite is due to geochemical conditions, a viewpoint tentatively held by [Dunn].
A very small number of calcium-poor leucophoenicite specimens occur without calcium-bearing species. These leucophoenicites are very uncommon; they occur in two types of assemblages:
1. With franklinite, willemite, and zincite in assemblages commonly devoid of other associated phases. If other silicate phases are present, they are tephroite, sonolite, or jerrygibbsite, the first two commonly in minor amounts.
2. With manganosite, zincite, jacobsite and hetaerolite, in coarse-textured specimens which are in large part manganosite (MnO) by bulk volume. This assemblage was examined in detail in search of the Mn-analogue of norbergite (MAN), which remains unknown in nature. The silicate phases in this assemblage are tephroite, sonolite, and Ca-poor leucophoenicite, which is the dominant silicate. (Dunn, 1995)

Location Found:

Franklin (Type Locality)

Year Discovered:

1899

Formula:

Mn₇²⁺(SiO₄)₃(OH)₂

Essential Elements:

Hydrogen, Manganese, Oxygen, Silicon

All Elements in Formula:

Hydrogen, Manganese, Oxygen, Silicon

IMA Status:

Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"

To find out more about this mineral at minDat's website, follow this link Leucophoenicite

References:

Dunn, Pete J. (1995). Franklin and Sterling Hill New Jersey: the world's most magnificent mineral deposits. Franklin, NJ.: The Franklin-Ogdensburg Mineralogical Society. p.352

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.64

The Picking Table References

	PT Issue and Page	Description / Comment
View Issue	V. 30, No, 2 - Fall 1989, pg. 18	Research Reports, Leucophoenicite Crystal Structure
View Issue	V. 27, No. 1 - Spring 1986, pg. 9	Mineral Notes Research Reports, Leucophoenicite
View Issue	V. 13, No. 1 - February 1972, pg. 10	Franklin Mineral Notes - Leucophoenicite
View Issue	V. 11, No. 1 - February 1970, pg. 6	Mineral Data - Sonolite, Alleghanyite, Leucophoenicite
View Issue	V. 9, No. 1 - February 1968, pg. 9	Mineralogical Data - Leucophoenicite
View Issue	V. 9, No. 1 - February 1968, pg. 15	The Exclusive Minerals of Franklin/Ogdensburg, N.J. (as of January 1968) by Frank Z. Edwards - Leucophoenicite

Images


Leucophoenicite (pink-tan) on green willemite from Franklin NJ. Photo by WP.


Leucophoenicite (tan, pink, with gemmy red crystals), calcite (white), and minor franklinite (black) from Franklin, NJ. 4 1/4" x 3" From the collection of, and photo by Robert A. Boymistruk.


Leucophoenicite crystals (gemmy red), and calcite (white) from Franklin, NJ. Field of view 1 1/2" x 1" From the collection of, and photo by Robert A. Boymistruk.

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