I was at a gem show and I saw some beautiful pendants. When I asked
about the stones in them, I was told they were “prenite.” I even had
him spell it and took a picture of it. They are a light green and
are polished as a cabochon, but I cannot find anything in my gem
books that tell me what they could even remotely be. Any ideas? He
definitely could not spell as I saw on other occasions. I’ve
attached a picture of the stone if that will help.The closest I could
come by picture and what I remember by seeing it, by Chrysocolla; but
then how do you get prenite from that? Since I really like the stone
and would like to buy some; I would like to know what I am buying
before buying it, if possible.
Possibly it’s prehnite. Leaving out the H would be an easy mistake.
(picture attachments don’t come through on the list, so can’t see
yours) Take a look at one uncut specimen on the mindat site:
…The Manual of Mineralogy does note that apophyllite, prehnite,
and chrysocolla are all closely related to and very difficult to
distinguish from the clorite group. In apophyllite, “the sheets of
tetrahedra are composed of four-fold and eight-fold rings”, rather
than six-fold rings, “linked by Ca, K, and F ions.” Another
complicated arrangement of layers of aluminum tetrahedra, as well as
the silicon tetrahedra, form the structure of prehnite…
i am pretty sure it is spelled prehnite, it some times has
tourmilated lines in there black or green, if you plug it in for a
search on yahoo there is a large section of definition for it it
reads it is a phylosylicate of calcium and aluminium, comes in green
to blue to white colors and is brittle, and there is a large offering
of it on ebay… i did buy some, in time I found out there is a huge
difference in quality.so be on the look out for that too. it mostly
comes from Africa but i had seen some from the far east, and i think
south America. the brittleness is a definite i had one large 30mm
cab start peel and crack on me while i was working and making a
setting for it. they are pretty cool greens but very finicky
I was told they were "prenite." I even had him spell it and took a
picture of it.
He didn’t spell it right. If you look for prehnite you’ll find lots
of
It’s a bit on the soft side (Mohs 6 - 6.5) but makes attractive
transparent to translucent cut stones in yellow-green and
brown-yellow. Cat’s-eye material is known. It’s usually cut as
cabochons but facet-grade material also occurs. It’s a calcium
aluminum silicate and is found in the U.S. and worldwide locations.
It is PREHNITE. It is fairly new to the world, discovered by a Dutch
Colonel in Africa, Tanzania. It often has black tourmaline running
thru it. I discovered it a year ago and just love it. Some sources
say 1970’s it was found.
I buy mine from Sunwest Silver in Albuquerque. They have the side
drilled shapes as well as faceted shapes. If you want pics, I would
be happy to send some. Most of it is drilled.
I had a friend put one in a ring for we, it just FEELS so great. The
stone has in inclusion, but love it anyway.
Prehnite is a mineral that is usually a waxy green colour and
hydrothermal in origin, similar to zeolites. It is quite hard [5 on
moh’s scale, same as apatite and stable, it is now commonly seen as
beads and cabochons. A lot of it used to come from the Deccan
volcanics in India, not sure where the cut stuff comes from. It is
named after Col von Prehn, an Austrian mineralogist.
Prehnite is one of those mildly attractive minerals that should not
find their way into jewelry…unless of course, you’d like to spend
time replacing it constantly. It is much too soft for most jewelry
wear, and, because it is not durable is technically not a gemstone.
it doesn’t fit the definition. Not that will stop anyone, but just
be aware it is fragile.
Mineralogically, it is a complex calcium alumino-silicate thet
crystallizes in the orthorhombic system, usually found as druses or
sub-spheroidal agglomerates. Usually it’s some shade of green to
yellowish green, but also can be colorless.
While it’s hardness is described as being around 6, it is extremely
brittle and cleaves easily as well. Probably fine for pendants.
Wayne Emery
The Gemcutter
"Bending Light Since 1975"
Prehnite: hardness 6-6.5, basic calcium aluminium silicate, color
yellow-green, brown-yellow. Suggest you get a book on
gemstones…recommend Gemstones of the World by Walter Schumann.
It is a good basic reference book.
Color Yellow Green
Calcium Aluminum Silicate (Ca2Al2Si3O10(OH)2)
Moh’s Hardness 6-6.5
Density 2.82-2.94
Cleavage Good
Refractive Index 1.611-1.669
No Pleochroism
Information from: Schumann; Gemstones of the World; Sterling
Publishing, New York
“Prehnite” is a fairly common mineral found as veins or cavity
filling as a result of hydrothermal alteration of some igneous rocks
in many areas worldwide. Here in northern Virginia it is a common
constituent of road gravel and construction rock qarried locally in
the diabase formations that filled Triassic basins. Zeolites
(stilbite, for example) and calcite are other minerals found
associated with prehnite. While the green color can be attractive,
the local material is too fractured to be of much use as gems. It is
also common in the New Jersey counterparts to our Virginia rock
quarries. The Palisades along the Hudson River are formed of this
kind of rock.
Prehnite is one of those mildly attractive minerals that should
not find their way into jewelry....unless of course, you'd like to
spend time replacing it constantly. It is much too soft for most
jewelry wear and, because it is not durable is technically not a
gemstone. it doesn't fit the definition. While it's hardness is
described as being around 6, it is extremely brittle and cleaves
easily as well. Probably fine for pendants.
I beg to differ, Wayne. Yes, it’s not super durable, but it’s not
super costly either. And if fragility is a big issue, then we better
stop calling opal a gemstone too. Or a number of others I can think
of that are also easily broken or abraded. (just for starters, how
about amber, chrome diopside, peridot, mabe pearls, and even many
emeralds, which though harder, are sometimes very fragile due to
existing inclusions. And the list can go on…) That classic
gemstone definition isn’t carved in stone in terms of just how hard
or durable a material must be. Only that it be durable enough for
it’s intended jewelry use, whatever that vague sort of statement may
mean. To catagorically state that it doesn’t fit the definition of a
gem for that defined reason is about as meaningless as the terms
precious and semiprecious…
I have a couple of friends who seem to be in love with the delicate
slightly transluscent pastel greens of Prehnite, and use it a lot.
One of them buys big cabs and coarsely facets the tops, setting them
still as cabs like big rose cuts. They look good in her silver
jewelry. I’ve seem some of these that have been worn frequently for
well over five years, and the stones, while a bit worn, aren’t unduly
so, and still look just fine.
I’d guess they may be more brittle seeming to the cutting wheel than
in normal wear, as to the best of my knowledge, she’s not had a
single one of these returned for stone breakage. She does take some
care in choosing stones, though, rejecting those that already have
significant cleavages. Once cut and set, they’re less likely to have
a problem, I think…
Try searching your gem books or the web for “Prehnite.” Typing in the
word in Yahoo yielded numerous results, but to answer your question,
Wikipedia has probably the most condensed description:
Prehnite is a phyllosilicate of calcium and aluminium with the
formula: Ca2Al(AlSi3O10)(OH)2. Limited Fe3+ substitutes for
aluminium in the structure. Prehnite crystallizes in the
orthorhombic crystal system. It is brittle with an uneven
fracture and a vitreous to pearly lustre. Its hardness is 6-6.5,
its specific gravity is 2.80-2.90 and its color varies from
light green to blue or white. It is translucent.
Though not a zeolite, it is found associated with them and with
datolite, calcite, etc. in veins and cavities of basaltic rocks,
sometimes in granites, syenites, or gneisses. It is an indicator
mineral of the prehnite-pumpellyite metamorphic facies. It was
first discovered in South Africa by Colonel Hendrik Von Prehn, an
early Dutch governor of the Cape of Good Hope colony. Prehnite
was the first mineral to be named after a person.
Is it expensive? someone once told me it was the "real" name for
"green garnet" is this true?
No, it isn’t expensive, and no it is not garnet. There are several
green garnets including Tsavorite and grossular green garnet, but not
Prehnite is not the “real” name for green garnet.
and prehnite, while neither expensive nor especially hard, is
beautiful; translucent, waxy, softly glowing… if you want a cabbed
stone that looks like the inside of a good green grape, go for it.
I’m a big fan. I think it would probably get a bit beaten up a few
years down the line if you set it in a ring that got a lot of wear,
but there are a lot of stones that you can say that for.
Prehnite is a quartz. As such, it is prone to fracture. While it is
not up there with diamonds in price, neither is it a cheap stone. It
can be either green or yellow. I have some yellow faceted roundels on
my web site if you want to look at a picture. Click on “gemstone
beads” then “quartz beads.”