Joined: Sun Oct 04, 2009 11:18 am Posts: 595 Location: Madrid, Spain
Nice shot! But it looks more like crystalline inclusions of other mineral, IMHO. Negative crystals in fact are cavities, where the form of the cavity corresponds to the form of the host mineral crystals. When you have a group of negative crystals, they can't be oriented in different directions like in the shot. Their outlines correspond to the crystal structure of the host mineral, so they should be oriented identically.
Joined: Sat Oct 13, 2007 9:03 am Posts: 109 Location: Italy
Thank you so much to everyone for have appreciated my shot... I'm a beginner about the photomicrography, but I'm fascinated from this little world... For Frank these are data of this photo:
Nikon D300 on trinocular Zeiss STEMI 2000C. exposure 1/8 Darkfield and fiber optical probe 12 different shots increasing the focus after I aligned and merge with Combined ZP software...
My first thought was that the inclusions were solid crystals because in the 3th book of photoatlas I found a very similar picture (prismatic apatite crystals)...But after this consideration I changed my opinion because with cross polarized filter I can't see the blink effect caused by birefringence of apatite crystals. I don't know Barbra the origin of this stone, because it was inside of old parcel of my grandfather, so I think that these sapphires have almost 50 years old... It's a cabuchon cut, with a wk, ml tone and slgB hue... I add a second photo of the same stone with a big gas bubble inside a cavity... The photo was take perpendicular to the cabuchon, it's possible that these ipotetic negative crystal are be oriented 120° or 60°?
_________________ Paolo Cerruti G.G. (GIA)
"When the winds of change blow, some people build walls and others build windmills" www.paolocerruti.it
Joined: Sun Oct 04, 2009 11:18 am Posts: 595 Location: Madrid, Spain
Frank wrote:
Great photography guys. How many shots did you stack to get this level of clarity?
The picture I posted is not mine, I posted the reference to the original site below. I usually make 3-12 shots for stacking, depending on the size of the object of interest.
wavewalker wrote:
Would the halos themselves be indicative of an expanding mineral inclusion instead of a negative crystal?
Yes, it's the most common case. But halos on fluid inclusions are possible too, they can form in cases of natural decrepitation of inclusions due to overheating or decompression.
paolocerruti wrote:
I add a second photo of the same stone with a big gas bubble inside a cavity... The photo was take perpendicular to the cabuchon, it's possible that these ipotetic negative crystal are be oriented 120° or 60°?
The cavity with the bubble looks quite different compared with the other inclusions. They don't seem to follow any specific pattern.
Additional comment: There is a particular case when "negative crystals" will not keep the symmetry of the host crystal at all. That will be the case of cavities formed after dissolved inclusions. Such inclusions don't fit to the strict definition of negative crystal but as a result we can have cavities with perfect crystal outlines inside of the host mineral, without any crystallographic correspondence. Quite a particular but not so uncommon case. I have one sample with perfect rhombohedral inclusions in quartz, some of them with intact calcite crystals and some with yellow hydrocarbon filling with bubbles! Sometimes you can see tiny fissures reaching that cavities and responsible for later fluid circulation, but such fissures can be also completely healed by later quartz precipitation! Other example of the same process is the well known Madagascan quartz with fluorite inclusions, where some inclusions are perfectly conserved (blue) and others are octahedron cavities (white). (this picture is mine! You can see some secondary fissures responsible for the dissolution of fluorite inclusions):
Joined: Thu Dec 13, 2007 3:42 pm Posts: 4091 Location: the Netherlands
Also, not every cavity (be it fluid or gas filled) has to be a negative crystal... If time has permitted it and the cavity is fluid filled a negative crystal may be the end result of 'healing' but usually there is a long road prior to that happening.
(general remark, I have no idea what those worms are)
Joined: Sun Oct 16, 2005 12:22 pm Posts: 21602 Location: San Francisco
As a possibly related sidebar. Dick Hughes recently said regarding what is considered a pardonable error:
Quote:
Seeing a crystal with a glassy tension halo in a sapphire, and thus believing it to be heat treated, but not locating a tiny CO2 bubble in a fingerprint (which would prove it is unheated).
Does anyone have a picture of such a CO2 bubble or additional information?
Joined: Sat Oct 13, 2007 9:03 am Posts: 109 Location: Italy
Barbra Voltaire wrote:
Does anyone have a picture of such a CO2 bubble or additional information?
Some "guru" about corundum inclusions can help us? Also about my first post question, I would like to know other opinions about my photos and if this inclusions are cavities or crystals... Mr Richard Hughes...can you help us?
_________________ Paolo Cerruti G.G. (GIA)
"When the winds of change blow, some people build walls and others build windmills" www.paolocerruti.it
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