Pyrophyllite
Aluminum
Silicate Hydroxide
AlSi2O5OH
Pyrophyllite finds the same use as talc, that is why most of the
countries combine the production figures of talc, steatite, etc. and
pyrophyllite together.
The
History Says
Pyrophyllite gets its name from the Greek words for fire and leaf as
in "fire-leaf". Phyllite is named after the Greek word for
leaf as well, in allusion to its flaky fracture. But pyrophyllite gets
its name from the fact that it exfoliates when water is driven off
upon heating, leaving a flaky mass. The flakes are actually the
silicate sheets that are a testament to pyrophyllite's structure.
The Present Scenario
There are actually two pyrophyllite minerals. One is monoclinic and
the other triclinic. Ordinarily they would be treated as two distinct
minerals, but their properties are identical and they are often
associated and intergrown. Separating them serves no purpose and the
two minerals are often considered as one; at least for now.
PYROPHYLLITE
is a secondary mineral of composition Al2O3.4SiO2.H2O,
containing 28.3% Al2O3, 66.7% SiO2
and 5% H2O. In appearance it looks like talc and in
physical properties also it is identical to talc. However, it differs
in chemical composition, as talc is a hydrous magnesium silicate
whereas pyrophyllite is hydrous aluminium silicate.
It is identified in hand specimen by imperfect micaceous structure.
It is opaque to translucent in thin section, appears to consist of
extremely fine grained talc and kaolinite. It is a little harder than
talc. Its sp. gr. is 2.8 to 2.9.
Pyrophyllite finds the same use as talc, that is why most of the
countries combine the production figures of talc, steatite, etc. and
pyrophyllite together. It would be proper to report separately the
production figures of these two minerals.
| Hardness |
Associated Minerals |
Fracture |
Colour |
characteristics |
Luster |
Field Indicators |
| 1 - 1.5 (soft
enough to be scratched by a fingernail). |
micas
sericite
chlorite
graphite
quartz
albite
barite
gypsum
andalusite
kyanite
sillimanite
lazulite
epidote |
uneven or
splintery |
usually white,
colorless, gray, yellow, pale green and/or blue. It can also be
stained brown by iron oxides |
Cleavage sheets
are flexible, but inelastic. A distinctive greasy feel to the touch |
greasy to dull,
but pearly on cleavage surfaces |
crystal habit,
color, cleavage, softness, aluminum test and feel. |
World
Resources
Many countries do not report the production of pyrophyllite
separately. It is included with talc. Thus, much useful information on
its occurrence, research, utilization and production has remained
obscure. Production, as far as known, has been reported from Canada,
Republic of Korea, the Rep. of South Africa and the USA.
Other occurrences in North Carolina are in Granville, Orange,
Alamance and Montgomery counties. Occurrences have also been noted in
Newfoundland, Nova Scotia, Vancouver island, South Mountain, and in
California. At present, the production comes mainly from Moore county,
North Carolina and San Diego county, California.
The pyrophyllite deposits of the USA are associated with tuffaceous
rocks which exhibit various stages of alteration. They are found to
occur as narrow bands or zones aligned with the cleavage, strike and
dip of the country rock.
Notable Occurrences
- Randolph
- Guilford
and Orange Counties
- North
Carolina
- Chesterfield
County
- South
Carolina
- Mariposa
County and San Bernardino County
- California
- Arizona
and Graves Mountain
- Georgia
- USA
as well as Belgium
- China
- Switzerland
- Mexico
- Minas
Gerais
- Brazil
- Sweden
- Ural
Mountains
- Russia
- Korea
- Japan
|
