One
of the frequent inclusions to see in a sapphire is phase inclusion, which is
not as such surprising to talk about. Although this phase inclusion must have
surprised Sir David Brewster, in 1823, when he first time saw the same.
In
routine testing IGI-GTL, Delhi received one yellow sapphire for testing. Microscope
analysis confirmed the stone to be natural and its other physical and optical
properties testing concluded the stone to be sapphire.
A
beautiful thing about that sapphire was one of its tabular negative crystal,
which was apparently visible even with unaided eyes and possessing vital area
of table. That was a three phase inclusion containing a black solid phase, a
gaseous phase and liquid (at the temperature <31.2°C) and two phase
containing a black solid phase and liquid (at the temperature >31.2°C).
Such
phase inclusions are encountered in sapphires from Sri Lanka. That black solid
phase was probably graphite (on the basis of visual observation and as reported
yet).
These
phase inclusions are generally filled with liquid CO2 and CO2 bubble. To check
the identity of liquid, I thought of doing temperature test i.e. to check that
at what temperature this gaseous phase gets vanished and the liquid gets
homogenized.
Visit http://youtu.be/6k2yDprC-Qo for clear video.
Critical angle of CO2 is 31.2°C (88.2°F), and if the gaseous phase persists even at the temperature greater then 31.2°C, that is not CO2 and is probably something else.
Critical angle of CO2 is 31.2°C (88.2°F), and if the gaseous phase persists even at the temperature greater then 31.2°C, that is not CO2 and is probably something else.
While
experimenting the same I thought of capturing it in my camera. I took a bowl of
cold water to get the stone’s temperature below 31.2°C (critical temperature of
CO2), and was expecting optic fiber light source to heat up the stone enough
(i.e. around 32°C and above) to homogenize liquid.
I
cooled the stone in water and put that under microscope. I waited for around 15
minutes but could not find bubble vanishing. First I thought if that liquid is
not CO2 and something else. Then I checked the optic fiber light source, but
that was at its full intensity. Then I checked the stone that was still cold to
feel. I noticed, air conditioner is just above my microscope, which was not
letting the stone to warm up. And also the metal tweezer holding the stone was
also cold due to some water droplets in its indented body.
I
dried the tweezer and rubbed the stone in my hands to warm it up, but unintentionally
I raised the temperature of the stone more than 31.2°C, and the liquid got
homogenized while the stone was in my hands only. While placing the stone back
on the microscope for observation, by mistake I dropped a small drop of water
on the stone. Fortunately when that drop fell on the stone I was looking the
stone through microscope. That small water drop developed spontaneous bubbling
of the liquid in that phase inclusion.
I
again warmed the stone and put that on microscope, this time I deliberately
cooled the metal tweezer with cold water and let the air conditioner do its job
of cooling the stone, as the room’s temperature was already around 25°C.
Within
seconds liquid of that negative cavity starts bubbling. Instead of capturing
the video of homogenization of CO2 liquid, I got the opportunity to capture
beautiful video of CO2 bubble’s evolution from liquid CO2. As if some champagne
bottle has been opened and thousands of bubbles were bursting inside the
sapphire. Probably this kind of bubbling is because the negative cavity was
quite big and while observation that was approximately parallel to ground, so
instead of evolution from a single point, bubbling is visible in large area.
The
frequent eruption of bubbles and homogenization of liquid at (approx.) 28 -
33°C, confirmed the phase to have CO2 liquid and CO2 gaseous phase. Although
there is possibility of some other material also with CO2.
Notice
the web like structure that forms just before the bubbles burst out. I don’t
know if that structure has something to suggest, maybe it’s only because of its
large flattened area parallel to ground. I wonder if someone has ever evidenced
such bubbling.
Comments
and suggestions are welcome.
(Photographs
and video are taken by the author.)
Meenakshi Chauhan
Indian Gemological Institute - Gem Testing Laboratory
Jhandewalan, Delhi
(Project of GJEPC)
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