WELCOME TO THE GEO-CLASS
Tonight's topic is Gems and Jewelry II: the Hard
Ornamental Materials
Again as with the soft materials almost every colored stone has
been used at one time or another for figurines, inlay, and other
articles of display as well as jewelry so rather than try to cover
all of them we are going to look at the most common and best known if
you have a question about something that I don't cover please let me
know and I'll see if I can find it in my resources also like before
we will generally work our way up the values from the least expensive
to the most. We will start with some Decorative Rock
Types, then the Epidotes followed by
Rhodonite, the Feldspars, the
Quartzes (Chalcedonies,
Massives, and Crystals),
Lapis, and the Jades.
The first group for tonight are some rocks
that we have mentioned in passing before that are sometimes colorful
enough to be carved or cut and polished. these are:
{P} *dramatic pause*
*{P} hides... "Sorry" *sheepish grin*
Rodingite
a course grained contact metamorphic rock that has grains of
silicates and calcareous minerals in pink browns, reds, and greens it
is often banded and may contain geodes.
Skarn:
another contact metamorphic rock containing carbonates (Calcareous
minerals), metal sulfides and oxides.
Calciphyre (Calc-silicates)
A third contact metamorphic rock that is generally light in color
with labradorite and with pink, yellow, green, blue and black grains
and zones or bands.
Eclogite
An extremely high grade metamorphic to igneous rock- especially
high pressure ranging from green to red and course grained - the main
minerals being garnet, pyroxene and quartz.
Griquaite
An igneous rock consisting of chrome diopside, pyrope garnet and
accessories and having a course grained red to green color
.
Garnet Peridotite
Garnet (red Pyrope) and Peridot (olivine-green) generally medium
grained peridot with large fractured garnets.
Epidotes
- there are 2 minerals and one rock in this group.
Clinoziosite
Ca2AL3Si3O12(OH)
H) 6.5 D) 3.4 - it forms pink to pale green masses and the best
massive material is found in Baja Calif.
Ziosite
Is the same material with a different crystal structure - it ranges
from white thru pale blue to green and violet. A pink Manganese
variety is known as thulite. While it is found in many places
including Wyoming, Austria, the Urals and Kenya it is the Tanzanian
deposits that are best known - these form rich green masses with red
rubies.
{A} ooohhhhh rubies
Unakite
A rock made of epidote (pistachio green) and pink feldspar - this is
found in the southeast of the US and in Zimbabwe.
Any questions on these?
{P} Nuh uh :>
Rhodonite:
H) 5.5-6.5 D)3.4-3.7 is the pink Manganese Silicate - this is used
instead of Rhodocrosite for things like wine cups and table tops that
are subject to acids or abrasion since it is acid resistant and
tougher and harder. The best pieces are marked with patterns of dark
Manganese oxides that create incredible patterns against the pink
background. The better material comes from Broken Hill Australia,
Langban Sweden, Daghezeta Tanzania, Sverdlovsk Russia, and Honshu
Japan. A darker zinc bearing variety is found at Franklin NJ.
any questions?
* P shakes her head...
<EW> not yet
Feldspars
Here there are 2 different groups the
Potassium (K) Spars and the
Plagioclase Feldspars.
Kspars are mostly white and nondescript but
the low temperature variety called
Microcline
can form in a number of other colors - the most common is pink -
hence the pink color of Granites in many cases. The important version
however is a chrome enhanced form called
Amazonite
or Amazonstone that is a bright green. The name comes from
the fact the variety was first found in pebbles and stones in the
Amazon river basin in Brazil - and much of the best material still
comes from there. Other good locations are Amelia County VA and Pikes
Peak CO - I have a number of fine small pieces from Amelia :>
Perthites are mixtures of Kspar and Plag that have formed
intermixed twins and fine patterns. These fine layers and intermixed
colors (pink and white-grey or green and white-grey) are very
attractive and sometimes the layers and crystal twins will separate
and reflect the light in patterns that are known as schiller.
Amazonite and perthite are used to make jewelry (cabachons) and to
make things like figurines and cups and containers - essential
anything you might carve. They are usually opaque so the are seldom
carved into thin or extremely hollow objects - like Jade is. The best
Perthites come from Dungannon Ontario. So some nice stuff up your way
P and some of your oldest stuff <G>
{P} :>
Plagioclase is actually a solid solution
of two minerals: albite (sodium Plag) and anorthite
(calcium plag) that form microscopic twins. When these two types are
in almost even amounts we have the type known as
Labradorite.
Then the twins are evenly split between the two minerals creating
a multitude of tiny reflective planes that create a schiller in blue
and green and sometimes gold. When there are inclusions of hematite
this material changes slightly to show a gold to red schiller and
color that is known as Sunstone.
Labradorite
is named for Labrador Canada where huge masses are found. In fact
these rocks are almost pure feldspar and some of the oldest rocks
found (3.2-3.5 BY) and are called Anorthosites. The best sites
for Sunstone are Tvedestsand and Hittero Norway and the Harts Range
N. Territory Australia. Anorthosite and labradorite are found in
Labrador (surprise surprise :>), several other sections of the
Canadian shield and the Adirondacks of NY. Some is also found in
Greenland adjacent to Labrador.
{A} the way it looks I almost expect it to feel greasy (I know
sounds dumb but it looks like it to me)
Yes and for almost the same reasons as the oil - the microscopic
twin planes split the light by sizes and reflect only selected colors
and since they are not all the same distance. between the colors
vary. At the American Museum in NYC there are several large (3 ft)
slabs on display that are incredible. Oh - these materials are more
normally used for things like table tops and inlay than for figurines
and containers.
any questions?
{P} Nope :>
{EW} no
{A} what makes it reflect the gold or yellow colors so ... well
tis almost glowing looking that is the reflection off of microscopic
plates of hematite - iron oxide. and it tends to give it a reddish or
yellowish color
{A} aaaahhhhh, k
{EW} ok :)
ok next group - everyone ready?
{P} Yep :>
{EW} yea
Anorthosite was already described, and the last is
Larvikite also known as alkaline feldspar syenite and like
Anorthosite its dominant mineral is labradorite - but it is richer in
dark minerals and sulfides than anorthosites.
any questions?
{P} Nope :>
{EW} is there a picture of that last one?
yes there will be <G>
{A} no questions on thi
Quartzes
the quartz family can be split into 3 subfamilies:
Chalcedonies (cryptocrystaline quartzes
(super microscopic crystals) )
Massive or microcrystaline quartzes
Crystal Quartzes
The general name for any crypto-quartz is
Chalcedony. This name comes from Ancient Chalcedon in Asia
Minor (Turkey) where it was once mined along with copper (where the
name actually comes from). Chalcedony ranges from translucent to
opaque and every color from white to black is possible. The main
varieties are:
Onyx - pure white or pure black or alternating bands of
black and white. Onyx comes from the Greek word for nail or claw
Sard - a pure blood red (and Sardonyx bands of sard and
onyx), Sard is named for Sardis also in Turkey
{EW} I don't know there was white onyx
sure is sons and I have some nice Easter eggs of it <G>
{P} I didn't even know that Onyx was a quartz... heh
{EW} I thought they are made of alabaster?
The name has been used for both materials and that has created
confusion - alabaster is much softer and should be kept separate -
but because its soft and easy to cut and polishes to look like onyx
it is often sold as it - welcome to gem faking 101 <G>
* *{S} grins.
*{A} grins
{EW} LOL
We will talk more about such things after covering the real things
ok?
{EW} ok :)
*{A} wonders if DH has the red on his web site? Tis not in my
books (pic that is)
Sard?
*{A} nods
No I don't hun - at least not yet
*{A} has not seen Sard before and is interested
Then I'll make a special effort to find a picture <G>
*{A} does not want to take up your time I can search next time I
am on a pc at work :)
Carnelian - orange red from iron inclusions this variety is
named after the Latin word for flesh which color it generally
resembles. Carnelian is found on some English beaches but the
majority of it and of sard and sardonyx now come from Brazil and
Uruguay
Plasma is a dark opaque green due to inclusions of green
silicates. if it is spotted with red-orange dots of iron oxides it is
called Bloodstone. Plasma and Bloodstone come primarily from
India and Brazil.
*{A} grins ... that's one of my all time fav stones. Tis
vvvvpretty not to mention cool looking
A second name is Heliotrope for red reflections this
material often produces when when turned to face the sun under water.
yes it is <G>
Chrysoprase is a translucent green chalcedony and gets its
color from traces of nickel in it the best Chrysoprase comes from the
Marlborough Mine in Queensland Australia other deposits are found in
Silesia Poland.
{P} Lotsa industry there :> natural resources... at least
that's what I was told...
Agate (named fore the Agate river in Sicily) is any
chalcedony that is layered or banded with several colors or bands or
that contains dendritic (root like) inclusions (normally of
manganese) a large number of varieties are named - mostly on the
bases of the patterns of the colors and dendrites.
Chert and Flint are two other varieties of
Chalcedony - chert being a light grey and generally translucent while
Flint is a dark grey to black and more opaque.
Petrified Wood and some types of fossil bone are
also chalcedony and are often polished (esp petrified wood) since
they retain the cellular structure of the tree or bone both can be
any type of the above materials thou carnelian and agates dominate.
Agate is found in many places in the US and petrified wood and
dinosaur bone are found in a number of places in the southwest and
recently formed petrified wood can be found in Wyoming at Yellowstone
(recently as in within the last 50 years <G>)
any questions on this group? or sub group :>
{A} um ... can you explain the last bit
Well I'll try to find the photo of it too but here goes :>
The geysers and hot springs of Yellowstone are rich in dissolved
silica - as they cool the silica normally precipitates out to form
the walls of the pools or the stream side formations but occasionally
a spring will flood a forest region nearby as the hot mineral rich
waters are absorbed by the wood of the trees they cool and react
exchanging silica for carbon and replacing the cells of the trees -
this kills the trees but the fluids are sucked up a ways creating a
white base of petrified wood below the wood of the tree.
{A} aaahhhh.
{A} now that would be something to see.
When the tree top falls it then falls into these mineral rich
waters and the reactions continue turning the entire trees into rocks
in a matter of years.
<*{S}> Interesting... Did not know the process was that
quick.
{P} Ohhhh, nifty :>
I'll scan a picture I have of this - they are called bobbysocks
trees for fairly obvious reasons <G>
{EW} I didn't know it was that quick either
{P} Hehe :>
{A} does it have the colors like other petrified woods?
It can - and the same thing can happen to bones of animals that
fall or are thrown/trapped into the springs. The trees are white on
the outside - the colors will prolly come later as iron and other
minerals are added slowly.
{A} true
ok any other questions?
{P} *noddles* My mother has a length of petrified wood... it's
fairly dark... very brownish... lovely though :>It's one of the
really old ones though...
yes they are I have several pieces of several different colors
{A} I have a nice piece too ... it has a "layer" of clear quartz
xstals on the "bark" tis neat to the touch.
{S} DH, there is an area of the south west, I think they call it
Painted Cliffs or something similar. It has a huge area of p wood and
is very interesting... How would a forest of such size become
saturated... It seems the springs would dry up or recede, or am I not
thinking clearly... Is the eruption of the mineral water usually a
continuous thing?
Its the Petrified Forest and it formed somewhat differently - here
the trees were knocked down into a sandy swamp and buried. Then as
waters flowed thru the sands they slowly replaced the wood with the
silica - same basic process but the start is very different.
{A} what about the length of time?
Much longer - thousands to millions of years instead of years to
thousands of years in Yellowstone. and we don't really know why the
trees were all knocked down - or even if it was a single event or
several close together.
Ok these quartzes are turned into almost anything you can imagine
so I'm not going to try and list them all :>
Microcrystaline Quartzes - in these the
crystal grains are almost visible rather than needing a high powered
microscope to see.
Jasper is the first of these and is really just course
grained Carnelian. It is found as the main ingredient in the banded
ironstones of the Lake Superior region. Iron mines and other similar
mines in Australia, Europe, and elsewhere. it is used in exactly the
same ways as carnelian.
Aventurine Quartz contains scales and flakes of mica,
hematite or goethite that give it a courser spangled green to
brownish yellow look. The green variety of Aventurine is rich in the
green chrome mica Fuschite and the best comes from India. A blue
variety is rich dumortierite and very attractive also.
Quartz that has replaced fibrous actinolite is known as
Tigerseye - the golden form is a complete replacement while
the blue form retains some of the blue actinolite needles. The blue
form (Falconseye) is primarily from South Africa.
And those are the microcrystaline quartzes any questions?
{P} No...
{EW} nope
{K} shakes head
Crystalline
Quartzes:
these are actually carvings and figurines etc made from single
crystals of Quartz. There are four varieties that are used with any
real frequency:
Rock
Crystal - clear Quartz.
The best known of the objects made from this are Crystal balls
<G> but other objects are made. Good localities include Minas
Gerais Brazil (xstals to 5 tons found), St. Gothard Switzerland,
Malagasy Republic, Tyrol Austria, Arkansas (near Magnet cove) and
many other places world wide.
Rose
Quartz
Most of this material is translucent but the best is transparent
pink. The reason for the color is still not known. Pala CA, Newry
Maine, and Minas Gerais are the best known localities but it is found
in many pegmatites around the world.
Citrine
This is a clear yellow variety and fairly rare - much of the
commercial material is made from treated Amethyst.
Amethyst
The purple form. The color comes from iron mixed in with the quartz
in trace amounts. The best amethysts are from Minas Gerais ( up to 12
inches long). Amethyst is found in many other places but crystals
large enough to carve are rare. Geodes filled with amethyst are often
cut and polished to turn them into display pieces or bookends and may
have both agate and amethyst in them. Unusual Ghost amethysts are
found in Amelia County VA - these have the outline of a deeper purple
crystal visible inside a larger lighter crystal. Some Ghost Rock
crystal is also found here.
any questions on these?
{P} No... but it still ticks me off that sapphires don't' come in
geode :>
*{A} thinks rubies and emeralds should too
Ah well hun
*{A} laughs
{EW} where is Minas Gerais?
Central Brazil - HW assignment for everyone - find a map of Brazil
and find the province of Minas Gerais - your going to be hearing a
lot about it in the next couple of weeks so you might as well all
find it <G>.
{P} Somewhere just behind my left elbow I think :>
*{P} grins at anna
<G>
{EW} LOL ;>
*{A} grins at Pangea
any more questions?
{P} Nope :>
{A} not on this
{EW} no
{K} nope
ok lets move on to the last three groups for tonight
Lapis
Lapis-Lazuli
(Lapis)
it is made of 3 different minerals and graded according to the which
is dominate. These are Hauyne, Sodalite and Lazurite in increasing
order of value.
Hauyne (Na, Ca)4-8(Al6
Si6)O24(So4,S)1-2
H)5.5-6 D)2.45 is never the primary mineral in Lapis but is often
present in small amounts. It is a dark blue to green in color.
Sodalite
Na4Al3(SiO4)3Cl
H)5.5-6 D)2.3 - It is a light to medium blue and normally forms
granular masses. The best localities for it include Bancroft Canada
and the Monteregion Hills of Quebec (one has section of almost pure
Sodalite), Litchfield Maine, and Magnet Cove AK
Lazurite
(Na,Ca)8(Al,Si)12O24(S,SO4)
H)5-5.5 D) 2.4 is the most valuable. It is a rich royal blue to
purple in color. The Badakhshan Afghanistan deposit is the world's
best and has been mined for over 6000 yrs.
*{P} was gonna buy a tube of ultramarine blue paint once [2 fl.
oz.] it had real lapis-lazuli ground into it... was $100 a tube...
eek - Yeah, it's expensive all right :>
Agreed :>
Other deposits are found at Mogok Burma, Siberia, Angola,
Labrador, Pakistan, California and Colorado. Lapis is a massive
material made of some combination of these minerals with flecks of
pyrite (golden yellow) and calcite (white points and streaks/bands).
and yes its very expensive -especially the true afghani material. The
material from the Monteregion hills ranges from a light blue to a
full deep blue and is fairly easy to work - I have a couple of small
pieces I collected back in '77 still I think. Lapis has been formed
into everything from chess pieces to thrones.
{A} thrones?
{P} Yeah, the Egyptians used it a lot no?
Ever hear of the Persian Peacock throne?
{EW} there was a lot of Lapis in king Tut's tomb
Yes there was
{EW} Shah of Iran?
Right
{A} aaahhh yes
The throne is several hundred years old and partly made of Lapis
any other questions?
{P} Not me :>
{K} nope
{EW} no not from us
Jade
{K} oh I like jade ;>
Jade
is actually 2 different minerals the massive fibrous form of the
amphibole actinolite is known as Nephrite; he other is the Pyroxene
Jadeite. Both are fibrous (microscopically to barely visible) tough,
hard (H= 6-7), dense (D=3-3.5) minerals.
Jadeite
is Na(Al, Fe)Si2O6
Jadeite is the rarer and more valuable while Nephrite is the typical
early Chinese and American jade. Jadeite is found in Tawmaw Burma
(which produces the finest known as Imperial Burmese), Tibet, Yunnan
China, Guatemala, California and Japan.
Nephrite is a variety of Actinolite: Ca2(Mg,
Fe)5(Si4O12(OH)2
Nephrite is found in Turkestan (Khotan, Kasgar, Yarkand), the Lake
Baikal region Siberia, Wyoming, Taiwan, British Columbia, California
New South Wales Australia, Zimbabwe, and New Zealand.
The colors for each range from pure white to pure black and every
color in between. The colors generally get darker with increasing
iron - but traces of other elements can create almost any color
imaginable. One of the photos I'll be including is a lavender Jade
dragon Vase from the Smithsonian Collection.
{EW} pink jade is pretty
{P} Ohhhh :>
Ok all of these are also used to make next week's topic -
Cabochon
Stones <G>
{P} WOOHOOO!!!! :>
{P} We're getting closer :>
yep and you will see your first rubies and sapphires next week
<G>
*{P} nudges anna "We'll go to the next swap meet, steal all our
birth stones, and then bugger off"
hmmmmm shall I do a special class on birth stones and such?
{P} Ahhh, now that would be interesting... I'd like to know about
the history of why stones were chosen and such :>
*{A} has another question about the p wood in Yellowstone
Ok what is it hun?
{A} has anyone studied the process there and do they have any
estimates at how long it takes?
Well the trees in the photo I'll put up (from 1989) were flooded
about 8-10 years earlier and the main destruction was done within a
year or two. The level of the top of the socks is still going up tho.
anything else?
{EW} not from us
*{P} shakes her head...
Ok then shall we adjourn till next week?
{P} It's okay by me :>
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