SCORZALITE FROM SOUTH DAKOTA:
A NEW OCCURRENCEI
W. T. PBcoRAANDJ. J' Fanov
Assrn.{ctThe occurrence, mineral association, chemical analysis, and physical properties ofscorzalite, (Fe", Mg)Alr(PQo,)r(OH)2, from the Victory mine near Custer, S' Dak', aresecond reported occurrence of this mineraldescribed. Scorzalite from this locality-thehas a Fe : Mg molecular ratio of 3 : 1, is richer in iron and has a higher specific gravity andhigher indices of refraction than the type scorzalite from Minas Gerais recently describedby the same authors.
INrnolucrroN

AND AcTNowTBoGMENTS

fn September Ig+7, during a visit with U. S. Geological Survey fieldparties under the direction of L. R. Page in the Black Hills of South
Dakota, the senior author acquired a blue mineral specimen which helater identified as scorzalite, the ferrous-iron member of the lazulitescorzalite isomorphous series. Because of the similarity of the material
to the type scorzalite from Minas Gerais, Brazil, the authors made adetailed study of the mineral from this new locality. M. H' Staatz andfrom the dumpJ. W. Adams kindly collected a large number of specimensof the Victory mine-the source of the first specimen examined'
The writers are grateful to a number of their colleaguesin the Sectionof Geochemistry and Petrology, U. S. Geological Survey, for assistancein various stages of the investigation.
OccunnorqcB
The Victory pegmatite mine is located about 2 miles northeast ofCuster, Custer County, S. Dak. In 1943-44this mine was one of the outstanding producers of sheet muscovite in the United States. L' R' Page,
who observed the mineral occurrence during mining operations, reports
the following account (personal communication) :,,The blue mineral now identified as scorzalite was seen in place only
on the 12O-footlevel, about 2Of.eetwest of the intersectionwith the crosscut from the mainshaft. Most of the rock containing scorzalite was excavated during mining operations for mica. The lower levels of the mineare inaccessibleat the present time and specimensof the mineral can beobtained only from the dump.
,,Mica-bearing pegmatite at the Victory mine is internally divided into'wallzone' (composed essentially of blocky plagioclase, quartz, anda1 Published by permission of the Director, u. s. Geological survey. Paper read before
the November 1948 annual meeting of the Mineralogical Society of America'685

686

W, T, PECORA AND J. J. FAHEYmuscovite) and a'core'(of perthite and quartz). scorzalite was foundprincipally in the wall zone, but some grains were also observed in thegranulite developed from schist where the two main pegmatites on the12O-footlevel merge discordantly. Triphylite is the only other phosphatemineral noted in the pegmatite and it is concentrated in the wall zonewith black tourmaline and ruby muscovite."
DBscnrprtvo MrNBnar,ocy
fn the dozens of hand specimens available, scorzalite occurs only inpegmatite with quartz, plagioclase, muscovite, tourmaline, and triphylite. The scorzalite is massive and so intimately intergrown with tourmaline, triphylite, and muscovite that small fragments, one centimeter
Tesrn 1. Crrputcer,Arer.vsns arn pnvsrclr pnoppnrros or.
Sconzar-rrnlnou Sourn Darora exo MrNes Gnnlrs(Analysesby J. J. Fahey)

AlrosFezOr
TiOz
FeO

MsoMnOZnOCaOPrOs
HrO+Totals
Mol. ratio,Fe":Mg.
Sp.gr., (+ .005)
c (colorless)0 (blue)
7 (blue)
2V (calculated)
Cleavage
Orientation
Twinning

Victory mineSouth Dakota

Corrego Frio
Minas Geraist

30.80
0.13
0 .1 01 7. 0 6
2.93
0 .1 030.87
0.54
0 .1 0
4.2s
0.11
U.TI

0.03
42.67
6 .1 00.02
42.90
5. 8 6

99.92

99.54

76:24

66:34

J.JZI

1.636
r.666
r.67661"(-)(110);good
Z:b;Xnear cmultiple

3.268
l .633
r.663
1.67362"(-)(110),good
Z : b ; X n e a rcmultiple

1 For original description see Pecoraand Fahey, Am. Mineral,.,34,83-93 (1949),
2 Determined with a fused quartz
Adams-Johnston pycnometer.

SCORZALITE FROM SOUTH DAKOTA

687

across, are rarely free from admixed minerals. Powdered scorzalite canbe purified using a heavy liquid (methylene iodide) and the electromagnetic separator.
The chemical analysis and physical properties of scorzalite from theVictory pegmatite are listed in Table 1, where they are compared withthose of scorzalitefrom Minas Gerais. The Victory scorzalite has a higher
molecular ratio of Fe": Mg, higher specificgravity, and higher indices ofrefraction. 'X-ray powder patterns of scorzalite and lazulite are identical.
A brief description of the associatedminerals is given below:
Tourmaline: massive and stubby, faceted crystals; color, blacklc,r:1.655; O:dark-gray green; specificgravity, 3.16.
Triphylite: massivel color, dark green; 9:1.690; 2V, very large;
Y:blue green.
Plagioclase: massive, coarsely twinned; composition almost pure albite;B:1.533.
Muscooite:two conspicuousvarieties, ruby and yellow; in zoned plates,
the ruby mica forms the core; the yellow mica also forms aggregateplates
that are younger in age sequencethan the ruby variety and the scorzalite;B (ruby):1.592; B (yellow) perceptibly lower than that of the rubyvariety.