Chemistry: K Mg3 AlSi3
O10 (OH)2, Potassium
magnesium aluminum silicate hydroxide.
Color: pale to dark brown.
Class: Silicates
Subclass: Phyllosilicates
Group: Micas
Crystal System: monoclinic
Cleavage: perfect in one direction
producing thin sheets or flakes.
Fracture: uneven
Hardness: 2.5 - 3.
Specific Gravity: is apx. 2.9+
Streak: white
Luster: vitreous to pearly
Transparency: crystals are transparent
to
translucent
PHYSICAL CHARACTERISTICS:
Phlogopite also called Magnesium Mica, is a relatively unknown, rare
member of the mica group. It is typically light to dark brown in color
and the dark brown virety may be difficult to distinguish from Biotite.
Phlogopite is essentially a complex magnesium, aluminium, iron silicate.
Which may show an asterism or six rayed star when a light source is
viewed through
a thin crystal. Caused, as in garnet, by iron inclusions.
These minerals are distinguished by the presence of the metallic minerals
potassium, iron, magnesium and aluminium. The color in both of these
micas is dependent on the amount
of iron. Phlogopite is iron poor and biotite is iron rich. Phlogopite
can darken color with an increase in iron content. Phlogopite is distinguished
from muscovite mica by its pale orange/brown colour, but is usually
not as dark in colour as biotite mica
Phlogopite is a member of the mica group of minerals. The term mica
describes a group of complex hydrous aluminium silicate minerals, which
form part of the phyllosilicate group. Crystals of mica normally exhibit
a perfect basal cleavage, and split easily into tough flexible sheets.
Phlogopite, like other micas, has a layered structure of magnesium aluminum
silicate sheets, weakly bonded together by layers of potassium ions.
These potassium ion layers produce the perfect cleavage.
There is considerable variation in the chemical composition of the mica
minerals. Phlogopite is common in dolomites and metamorphic limestones
(magnesium rich marbles). Also in some pegmatites. Where as, Biotite
tends to form in a wider range of conditions. Associated minerals are
dolomitic marbles, hornblende, garnets and schorl.
Crystal habits include tabular to prismatic crystals with a prominant
pinacoid termination. Phlogopite's four prism faces and two pinacoid
faces can form a pseudo-hexagonal crystal wich is also called a Book.
It can also occur as lamellar or granular rock forming masses.
USES:
Used today mostly as rare mineral Specimens. Phlogopite was a little
rarer member than the other micas. But not uncommon. It was mined for
it's good heat and electrical insulating properties. which are
superior to other micas.
LOCALITIES:
We have some nice specimens from Kokscha Valley, Badakshan, Afghanistan.
Other areas we have seen nice crystals come from are. Ontario and Quebec,
Canada. Phlogopite was known both from the Franklin Marble pit and the
orebodies at Franklin and Sterling Hill, New Jersey. Phlogopite from
Franklin was first described, as mica by Silliman in 1850. There are
other Us locations as well as many locallities in Europe and Russia.
One of the largest deposits on earth. Occurs in the northwestern part
of the Kola Peninsula, Russia.
HISTORY & FACTS:
The word Phlogopite comes from the Greek flogopos - "resembling
fire."
Top
Click
here to see our Phlogopite Specimen
Click here for Mica Group Info
