I am Steve Moriarty I'm coming to you from MoreGems.com and we also have a
retail store on the square in Crown Point, IN ( Moriarty's Gem Art ) Today I want to discuss a
underused piece of equipment that can be very valuable particularly with rough
stones we've discussed a refractometer before it is the most valuable tool when
you're dealing with cut stones but it's not useful at all for rough stones
because you don't have a flat surface to get a refractive index on so specific
gravity is a comparison of a stone weight in water as compared to a stones
weight in air so the equipment here I'll show you you of course need a an
accurate scale and for this equipment you need a scale large enough that this
this holder will slide on it
so that's the support structure and this device goes on the scale and we have a
beaker with distilled water and the hanger to support it in the water
without touching the container so that's the basic setup some run a specific
gravity test so the gems we're going to work with today I say this is good for
rough gems cut gems and can even be used for metals it's helpful but because
metals are a mix of things much like rocks are like turquoise they're a mix
of materials so depending on what the mix is it can vary the specific gravity
so this is really best for minerals that are pure and it'll give you a very
specific number so the stones were going to test today first of all here's a cut
gem this is
cut glue jam and then we have a Bluegreen piece of rough see the color
to transparent piece of rough next one is kind of a violet blue piece as good
crystal form and then another cut gem
kind of a peachy color could be topaz could be a sapphire could be a garnet
and a violinist red piece of rough
in this
piece of gold material doesn't have a cleavage plane which will be an
indication of what it might be and the last one is a kind of pink stone water
worn pebble so to start the test we need to take each one of these stones first
we have to zero the scale out I'm going to put it on carats and then we weigh
each stone in air so this one weighs thirteen point one seven carats so I
write down the weight and air and I'm going to do all these stones and air
first so this blue green rough weighs 75 point
make sure zero so 74 94 so next a violet blue rough please 40 point 8 3 carats
and the peach colored gem weighs nine point four five carats
the red ruffed weighs twelve point eight one I should add and the golden orange
ruff weighs 140 162 and the pink stone weighs five point two seven carats so
next we weigh them in the water now you have to make sure that the the hanger
does not touch the sides or touch the bottom of the container and just drop
the stone on it it weighs three point nine four carat is
the weight in water
and the golden orange ruff weighs 106 93 you do have to make sure that it's under
it's a large piece that it is submerged
and the red rough weighs 940
3-0 this
okay waste 9:45
just need to reweigh it I didn't write this one down, it weighs 1280 and air
and the peach cut gem weighs nine point six point nine seven and that compares
to 945 when it was weighed in air
and the violet blue rough 2863 and this way 40.8 3 in air
and the blue-green rock weighs 51.47 and the blue-green gem weighs 10.35 and it
weighed thirteen point one seven in air so the next step is to take these
numbers you take the weight in air and subtract the weight that you got in
water and then you divide the weight and air by the difference that you got
subtracting the weight and air from the weight and water (Weight in Air)/(Weight in air - Weight in Water) and this will give you
the specific gravity of the gym and then we'll look up the number in the book and
it should help it should be an identification for the gem so let me run
these figures and we'll be right back with you so I've done the calculations
on all these gyms and here's the chart to show you how it's done so we had the
weight and air and then we weighed it in water which it's a lower number and then
we took the difference between the weight and air and weight and water so
we subtracted be from a and that gave us this difference and then we took the
weight and air divided it by the difference of the waiting there and
weight in water and it gave us this number which is now our specific gravity
so from here we go to a specific gravity chart which you'll find online or this
is handbook of gemstone identification and
this will give us the list of all the specific gravities for different gems so
if we take our first gem which was this blue stone and we look at the number we
got which was four point six seven if I go to the specific gravity Table four
point six seven the closest number is four point seven oh but it also has plus
and minus 0.03 which brings us into that four point six seven and it would be hi
zircon so this is a blue zircon is what this gem is so very accurate
identification of that one the next one is the blue green rough so that was this
piece and the specific gravity of this gem was three point one nine so if we go
to the charts three point one nine gives us there's two or three of them at the
three point one eight which would be fluorite apatite or spa janine fluoride
would be a possibility but I know this gem to be apatite exactly what you would
do to separate from there I'm not sure but we do get down to a couple of gems
that it could be fluoride being very soft you could do a hardness test this
is soft Jen - but fluorides very soft so it's pretty much accurately identified
that gem the next one is our violet blue rough
that would be the stone and we get a specific gravity on this one up three
point three four six three point three four could be jadeite I know it's not
jadeite could be peridot I'm pretty sure it's not peridot doesn't come this color
so the closest is three point three which is eyesight could be diabetes
Quanah looping so there is more stones do more tea right so there's several
gems but it's gotten this closer this one I know to be Zoey's eyes the numbers
slightly off but very close the next one is the peach cut gem this gem and the
refractive index on it was three point eight one and three point eight one on
the chart shows us that it's somewhere azurite rhodolite andridite would be
the three options and because the garnets tend to mix with each other they
do give some variation in the number and and this is actually a garnet somewhat
akin to rota light it is a mixture of several stones this is a malaya or
mehandi garnet the next one red rough
which is this town and it gave us the refractive index of 3.8 - very similar
to last known and that's because it is rhodolite garnet which in the charts
gives us a number of 3.84 with some variations so this is row light and red
light actually is a mix of garnets - so it can vary slightly next town would be
the golden orange rock this big piece and its specific gravity was 4.08 and
4.08 the closest is 405 which is either almond ight or sailor right and because
it does have a perfect cleavage plane I know it's not almond alley so it is Fela
right this comes from Spain and the last one this pinkish piece of rough the
specific gravity ended up being 3.99 and the options for 3.99 would be zircon or
corundum would be the two primary choices Or gano spinel this one is
corundum zircon typically we don't see this color gano spinel would not be this
color so it leaves us with corundum so it's accurately identified this so this
is a very good tool for particularly rough because you don't have a lot of
tools to identify rough material so this would be good for travel if I could get
this in my suitcase takes a pretty big scale to carry along with you but it is
a very accurate tool and I recommend it use for many things so if you want to
see more instructional videos you can go to our YouTube channel moregems or come
visit us on the square in Crown Point or moregems.com online.
okay thank you for watching