Chlorophoenicite |
| (Mn,Zn)3As2O8.7(Mn,Zn)(OH)2 |
| Monoclinic |
| a : b : c = 2.357 : 1 : 2.153; b = 74° 26' |
Forms
c(001), a(100), s(106), r(102), k(104), h(203), and p(111)
Habit
Chlorophoenicite forms slender crystals, as much as a third of an inch long, prismatic
parallel to the orthoaxis. The crystals are deeply striated parallel to their length, the
orthodome zone is somewhat warped, and the terminal faces, of which there are not more
than two on any crystal, are etched and give poor readings; hence the crystallographic
data are poor. The elements adopted were derived from the measurement of 14 crystals,
which showed a wide range in individual angles. The form series is peculiar, and the
position selected was that giving the simplest indices for the best-developed forms. The
cleavage plane, generally the brightest face of the orthodome zone, was taken as the
orthopinacoid and the next best face as the basal pinacoid. The epidote-like habit is
shown in figure 192, which is taken from the paper by Foshag, Berman, and Gage (946).
| Figure 192 Crystal of chlorophoenicite showing the forms c(001), a(100), s(106), r(102), k(104), h(203), and p(111). Franklin. A, Plan; B, clinographic projection. |
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In it the point of view is changed from the usual one in order to show both terminal faces.
Physical properties
Chlorophoenicite is light grayish green in natural light but is pink or light
purplish red in artificial light, hence its name, from Greek words for those
colors. It is optically biaxial and negative; the plane of the optic axes
is the plane of symmetry; 2V = 83° ±2° ; r > v (strong); a
= 1.682, b = 1.690,
g = 1.697. The
cleavage is good parallel to the orthopinacoid, the luster is vitreous to
pearly, especially on cleavage surfaces, and the hardness is 3 to 3.5. The
specific gravity is 3.46.
Composition
Chlorophoenicite is a hydrous manganese-zinc arsenate containing some magnesium,
calcium, and iron.
|
Percent |
Ratio |
||
| MnO |
34.46 |
0.486 |
|
| ZnO |
29.72 |
0.365 |
|
| FeO |
0.48 |
0.007 |
0.951* = 10 x 0.095 |
| MgO |
1.34 |
0.033 |
|
| CaO |
3.36 |
0.060 |
|
| As2O5 |
19.24 |
0.084 |
= 1 x 0.084 |
| H2O |
11.60 |
0.644 |
= 7 x 0.092 |
|
100.20 |
|||
| [* Figure reflects 0.486 + 0.365 + 0.007 + 0.033 + 0.060 values shown.] |
The analysis yields the empirical formula 10(Mn,Zn).As2O5.7H2O,7H20, although the arsenic is rather low for that composition. The formula may be interpreted as (Mn,Zn)3As2O8.7(Mn,Zn)(OH)2. Heated in the closed tube the mineral gives off water at a low temperature and turns black with a brilliant luster but does not fuse. Before the blowpipe it is fusible with difficulty, without decrepitation.
Occurrence
Chlorophoenicite, discovered by Gage in 1923, was described in a preliminary
paper by Foshag and Gage (231) and more fully by Foshag, Berman, and Gage
in 1924. It was first found in pillars of ore between the 500- and 600-foot
levels in the mine at Franklin, where crystals of it were implanted on the
surfaces of cracks and slickensides in massive franklinite-willemite ore,
associated with crystals of leucophoenicite and calcite and more rarely of
tephroite. Its slender needles resemble rather closely crystals of transparent
willemite.
Chlorophoenicite has also been found in radiate aggregates of acicular crystals on the 900-foot level in the mine at Sterling Hill, associated with calcite and barite.
In 1928 Palache (257) described flattened prisms that were doubtfully identified as clinozoisite, though their optical characters did not agree very closely with those of that mineral. Later study by Bauer and Berman (273) has shown that the crystals are undoubtedly chlorophoenicite, and that name should be substituted for clinozoisite in lists of Franklin minerals.
Another interesting occurrence of chlorophoenicite was seen in a single specimen from Franklin. In a cavity in a carbonate vein is an aggregate of needles of chlorophoenicite, thin bundles of needles being grouped with great regularity as a six-rayed star. Although this may be a twin aggregate, it seems more likely that the growth was controlled by a calcite crystal that was partly replaced along definite crystallographic directions by chlorophoenicite and then wholly removed, leaving this skeletal growth of fibers.
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Website
© by Herb Yeates 1997-2006.
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page created: August 12, 2006 5:53 PM
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