UNAKITE
UNAKITE
A. Unakite
polished paper weight (width - 6.7 cm) from the type area in the Unaka
range of the Southern Blue Ridge Province near the Tennessee-North
Carolina line. This piece was given to me by my dear friend Anna
Jonas Stose (1881-1974), who mapped the geology of much of the southern
Blue Ridge Province. R.V. Dietrich
collection. (© photo by Dick
Dietrich)
B. Unakite.
Polished gemstones (large cabochon, greater axis - 3.7 cm) fashioned
from material
from Augusta County, Virginia. This material has a so-to-speak intermediate grain size and
contains more epidote per unit volume than the specimen shown in
"A." As indicated by the faceted
stones (upper left and right), some masses of alkali
feldspar and epidote within the rock from this locality (and from several
other
localities!) are large enough
to
yield cut stones that consist wholly, or nearly so, of only epidote or
alkali
feldspar. The small cabachons are arranged to show different
percentages of the two constituents -- left to right the feldspar
content decreases as the epidote content increases.
R.V. Dietrich collection. (© photo by Dick
Dietrich)
DESCRIPTIONs: Although unakite is frequently
and widely referred to
as an epidotized granite (which seems to be the origin of the type
locality rock and those shown in Figures A & B), many items labeled unakite in the market
place have quite different origins and overall
compositions. Indeed, several so-labeled marketplace items
consist largely of an alkali feldspar and epidote with little if any
quartz,
a specific constituent of granite. Properties of the typical
feldspar of these rocks -- i.e.,
deep salmon colored alkali feldspar -- and of quartz (typically
nearly colorless and commonly microcrystalline) are given under the
Description
subheading in the GRANITE entry. Properties
of epidote, as it occurs in these
rocks, AND a general description of the rocks called unakite
follow:
Epidote Ca2(Fe,Al)Al2(Si2O7)(SiO4)O(OH):
Color -
mixture of pistachio (bilious, to
me)
yellowish green
H. 6
S.G. 3.4 - 3.48
Light transmission -
opaque
Luster - pearly to subvitreous
Breakage - irregular
Miscellaneous -
typically massive -- i.e.,
finely crystalline.
Unakite:
Color - mixture of pistachio (bilious, to
me)
yellowish green (epidote) and salmon pink (feldspar) plus or minus
nearly colorless (quartz)
H. (effective hardness) 6 - 7
S.G. 2.55 - 2.85
Light transmission -
opaque
Luster - pearly to subvitreous,
depending upon percentages of constituents and what part(s) of
the rock's surface is viewed
Breakage - highly irregular
Miscellaneous -
color mixture is distinctive; epidote occurs as veinlike masses
as well as fairly discrete grains, most of which consist of massive
material, in some of these rocks; the feldspar in some of these
rocks appears to be partially epidotized; the rock at some
localities is foliated, in some places an augen gneiss.
OTHER NAME:
- Epidotized granite
- apparently
unnamed, a rather attractive gemrock that appears to have this general
composition -- i.e., it is said to consist largely of epidote and
potassium feldspar -- is illustrated by Pulkkinen (2013 -- Figure 3,
upper left & p.c., 13 May 2013).
USES: Beads (tumbled pieces as well as
spheres and other fashioned shapes); tumbled chips, cabochons,
faceted, freeforms and
scarabs for
jewelry -- in particular for relatively large pieces in which one can
see the contrasting green and pink constituents to best
advantage, but also in rings; eggs, spheres, pyramids, hearts,
wands and
palmstones;
carvings, both small for such things as pendants and larger for
curios; small boxes and other containers; paperweights;
etc.
Some unakite has been used as tile -- e.g., on the main
terrace of the National Museum of Natural History (Smithsonian
Institution) in Washington, D.C.
OCCURRENCES: Unakite per se occurs as parts of granitic
masses --
commonly small masses such as dikes and lenses -- that have undergone
epidotization, with the epidote representing diverse alteration and/or
replacement processes; it also as cobbles and pebbles in
unconsolidated sediments derived at least in part from such
masses. The above described virtually quartz-free unakite-like
rocks have, I suspect, several diverse origins, none of which I
have seen described well enough professional publications to warrant
summarizing herein.
NOTEWORTHY LOCALITIES: Epidotized rocks are relatively
common. Unakite and unakite-like rocks have been recovered from
several places in
the Blue Ridge Province of the eastern United States -- e.g.,
in Madison (e.g., near Bluff)
and Mitchell counties, North Carolina; Unicoi County,
Tennessee; and Augusta and Roanoke counties, Virginia. I have
seen several pebbles, cobbles, and boulders of similar rocks in glacial
drift and along Great Lake
beaches in, for example, Michigan. On the basis of personal
observations of many Blue Ridge occurrences and several cobbles (etc.)
in unconsolidated materials of the upper midwestern states, I consider
some of the material from the Airpoint granite of
Roanoke County, Virginia to be top-grade gemrock rough, with rocks from
none of the other listed localities
-- including the type area in Madison County, North Carolina -- to be
even
close seconds so far as the quality one would like to use as gemrock rough. I realize, however,
that several will not agree with my evaluation, AND, my statement does
not, of course, refer to occurrences elsewhere in the world or even to
those in
the Blue Ridge Province of the eastern United States that I have not
visited. For example, I have not, so far as
I know, seen specimens
or things fashioned from the localities the localities recorded on the www.ontariominerals.com/ontario_lapidary
web site: "The
feldspar-epidote mixture known as 'unakite' is found at the Canada
Radium Mine; what is apparently the same mixture, [but] given the name
"mylonite", is mentioned from Monk Road, Bancroft, by Leach, 1964, p.9
[see Appendix C]. [and] David Millis (1999) mentions the
feldspar-epidote combination 'unakite', fine cutting material with good
color, from the Marmora Quarry, near Madoc [,Ontario, Canada]."
Although much of
the unakite-like material marketed as unakite is said to come from
Brazil, China and South Africa, I have been unable to find well
documented reports that give any localities other than Upinton and
Neilersdrif, Northern Cape Province, South Africa.
REMARKS: Unakite was named for
occurrences in the Unaka range of the Great Smoky region in the Blue
Ridge province of eastern Tennessee and western North Carolina by
Bradley (1874), who called it "Unakyte, an epidotic rock." (I
suspect his Bradley's use of the -yte suffix, rather than the -ite
suffix was in
deference to J.D. Dana's suggestion that such could be used to
distinguish rock names from mineral names.) However, as
mentioned under the DESCRIPTION
subheading, this designation has been extended (dishonored?) -- especially in the market place
--
to include several rocks that are characterized by deep salmon colored
feldspar and green epidote but contain little, if any, quartz.
Although I would prefer that these
virtually quartz-free rocks be called unakite-like or, at least,
"unakite," I feel sure this will not come
to pass. So, it seems that we shall have to live with unakites and
unakites that differ from accepted nomenclature usage.
Along this line, two other rocks -- okkolite
and an otherwise unnamed epidote-quartz
rock -- seem noteworthy here: 1.Okkolite,
apparently made up
largely of
diversely colored epidote grains, is from near Keimoes, Cape of Good
Hope Province, South
Africa, where it has been used as a gemrock.
2.The epidote-quartz rock, is said to be from Sonora,
Mexico and to have been fashioned into some fine cabochons.
Both of these gemrocks are likely epidosites -- i.e., rocks made up largely of
epidote, as the major component, and quartz. And, I suspect that
at least the one from Mexico might resemble stones fashioned from
epidote-rich portions of unakite (e.g.,
the faceted one in the upper right of Figure B). Indeed,
one wonders if either, or both, of these rocks is spatially associated
with unakite: Epidosite and unakite have been found so related
near Fisher's Gap, in the Blue Ridge Povince of Madison County,
Virginia (Phalen, 1903).
A
lesson for collectors: I still bear a
scar from a deep cut and loss of
much blood suffered from a small flying disc broken from a student's
apparently improperly tempered hammer while she was trying to get a
good
sample of unakite from the Airpoint mass southwest of Roanoke,
Virginia. Indeed, several years later, an operation was necessary
to remove the
metal disc. The important aspect of this story is that several good samples
were loose on the ground
adjacent to the exposure, just so-to-speak waiting to be collected -- i.e. no hammering was required to
get good specimens. So,
I
mention this episode to
emphasize two things: 1.Fine specimens are often loose, and thus
readily available, near
outcrops and road cuts. and 2.One should always be
extremely careful
when using
hammers, chisels, and other tools to remove rocks from exposures
or, I should add, even when breaking pieces of loose rubble.
According to
information supplied
me by those familiar with efforts to establish official state
minerals,
rocks, and gemstones for Virginia,
listings
of unakite as the state gemstone of Virginia (e.g., on the web
site
www.jackgolightly.com) are erroneous. And, I suspect the same can
be said about listings of unakite as the "official stone" for South
Carolina (e.g., on web
site wwwdesigner.cabs.com).
SIMULANTS:
None that I have seen or seen described.
REFERENCES: No general
reference. VanLandingham, 1962, pts.3 & 4; Owens, 1977.
R. V. Dietrich © 2015
Last
update: 8 July 2013
web page created by Emmett Mason