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 Post subject: Help needed in filling chart
PostPosted: Thu Oct 09, 2008 11:10 am 
In preparation for the FGA exam in January, I'm filling in a chart of properties of various common materials.

However, I have loads of gaps:

Colouring agent: Iolite, Sinhalite, Scapolite(Yellow), Kyanite, Andalusite

SWUV/LWUV: Chrome diopside, Blue Topaz(treated), Sinhalite

CCF: Chrome diopside, Iolite, Tanzanite, Kyanite, Spessartine

Crystal habit: Iolite

Spectrum: Tanzanite

Are garnets ever etched or striated?
Does asterism only ever occur in almandine garnets?
Does sphene ever show asterism/chatoyancy effects?
What impurities can colour natural blue spinel?

Cheers,


Last edited by Kyriakin on Thu Oct 09, 2008 12:33 pm, edited 5 times in total.

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PostPosted: Thu Oct 09, 2008 12:16 pm 
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Hmm .. I'll try to help as I can:

Coloring agents:

Iolite: Iron
Sinhalite: Iron
Scapolite (yellow): color centers
Kyanite: Blue: Iron; Green: Vanadium
Andalusite: Green: Manganese; Brown-Green: Charge transfers of titanium and iron-oxygen ion pairs

SWUV/LWUV:

Chrome diopside: LW: Green; SW: Inert
Topaz: What color????? The reactions vary

CCF: I don't know what this means :oops:

Crystal Habit: Iolite: Orthorhombic

Spectrum: Tanzanite: This depends upon the direction you're looking in.


Almandite garnets are the only ones I know that show asterism, but never say never! :P

Sphene has no phenomena ... again, until someone finds one that does!

Don't know about the garnets etching or striated :oops:

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PostPosted: Thu Oct 09, 2008 12:24 pm 
Thanks, that's filled in quite a few gaps.

Apologies, CCF meant Chelsea Colour Filter, and Topaz-blue UV might be most interesting (from an Aquamarine point of view).

With the Iolite I meant the shape of it's crystals when found - prism, tabular, only as aluvial pebbles etc.

If blue Kyanite and Sinhalite is iron-allochromatic I assume I can put them down as LW/SW inert too?


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PostPosted: Thu Oct 09, 2008 12:25 pm 
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Hi

i had a whole thing typed and then ACCIDENTALLY erased #-o , good thing morning dove , i didnt want to have to rewrite it all :cry:

ccf = chelsea filter reaction :wink:
chrome diopside does turn red
Dr Hanneman has a filter to help identify tanzanite

iolite cystal habit is massive , prisms

blue topaz UVLW : inert to weak , yellow green
UVSW : inert to weak yellow gree but lighter then LW


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PostPosted: Thu Oct 09, 2008 1:04 pm 
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Thanks for filling in the blanks, Dragonstek :D .

And, no offense to Dr. Hanneman, but you don't need a "special" filter for tanzanite ... a regular Chelsea Filter and your dichroscope will do. :)

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PostPosted: Thu Oct 09, 2008 2:39 pm 
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Kyriakin, altough I understand your wish to grasp the lot in total I can assure you that none of the requested info will be topic of examination in a foundation examination.

the best advice I can give you is:

practise the past exams again, and again and again... Also have those homework assignments memorized fully.

If I get it right, he only question MODO and Dragon haven't answered yet is that of the iolite habit. It would be: technically orthorombic prisms, but usually fractured shapeless pieces or rounded by wear and tear...


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PostPosted: Thu Oct 09, 2008 3:02 pm 
Spauwe wrote:
Kyriakin, altough I understand your wish to grasp the lot in total I can assure you that none of the requested info will be topic of examination in a foundation examination.

the best advice I can give you is:

practise the past exams again, and again and again... Also have those homework assignments memorized fully.

If I get it right, he only question MODO and Dragon haven't answered yet is that of the iolite habit. It would be: technically orthorombic prisms, but usually fractured shapeless pieces or rounded by wear and tear...


Oh no, I done the Foundation. Got an A so won't need to re-sit it at all. This is for the Diploma exam.

Sphene, kunzy, Sinhalite, diopside, scap etc. all seem to rear their heads in the diploma course.

A lot of it is the generic scapolite/citrine and peridot/sinhalite questions that can be learned like a robot, but I figured I mayaswell throw some additional info in as well. Can't hurt to know it..

Always useful for when one of these vague "name/describe 5 yellow gem material"-type questions come up.

Probably my fault for sticking this in the beginners section. Although I still feel like a beginner..


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PostPosted: Thu Oct 09, 2008 3:24 pm 
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Oooowww, that's what one gets from hasty reading, you did state FGA exam, just didn't pick it up.

well the advise remains the same :) And very true, if you can add all those additional items an A will be there waiting for you. I found that writing down all the obvious answers took me the 3 hours they give you, watch out for elaborating too much and getting yourself into time trouble. Write down the core first and when you have the time spice it up with all the 'A+ facts'.

Like with the yellows and their ID:

zircon --> OTL RI but diagnostic 653nm line in spectrum
Citrine---> RI 1.546-1.565 U+ and bulls eye
scapolite--> similar RI to citrine but U-
etc etc

when you have time left you can elaborate a bit but I wouldn't push it... It's the vitals they are looking for.

Since you're doing the diploma exam one more thing:
You're allowed to have your handbook on the table while doing the practical... make use of that!!! Know that little book inside out including page numbers so you can flip to relevant pages quickly. 3.5 hours for 24 stones is not a lot of time, practise till perfect, you have an average of 8.5 minutes to ID AND REPORT each stone. That's not a lot of time but certainly achievable...

Best wishes!


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PostPosted: Thu Oct 09, 2008 3:33 pm 
Yea, I need to see an example of a good clinical answer paper, just to re-assure me that bullet-point style answering does do the job. As a slow writer, it would be very useful.

The english school education system seems to award for bulk of writing over quality, and people can be lead into believing that an answer is sub-standard unless it is a solid block of writing.

I assume this practical exam rewards for correct observations, even if the conclusions drawn (i.e. the identities) are wrong?

Also, it seems stating the obvious is important in the practicals. Even colour and cut seem to be worth easy marks. Lustre too...


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PostPosted: Thu Oct 09, 2008 3:35 pm 
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HI

Congrads on the A , and welcome :smt006

i too suffer from wanting to have all my bases covered , just incase , i hate to know there info out there and i just didnt bother to find it :wink:

no worries , we can all learn from questions asked , and thank you , i learned something too

good luck on your diploma exam

spauwe right , i get myself bogged down with info i may not need , but it nice to know :D


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PostPosted: Thu Oct 09, 2008 3:45 pm 
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grab your practical handbook and read page 163 to 176... for an answer to your practical exam questions. Do state the obvious, you're a gemmologist writing reports about his/her gem ID. Follow logic steps, one test result will make the 'group of possibles' smaller pick the appropriate test to follow up and narrow down your possibilities even further... don't start grabbing your ccf when you have a colourless stone in front of you :D

I think well explained diagrams are the way to go whenever possible with the theory exam. Bulk text doesn't sound appealing, things are better written down sytematically:

facts
--> short explanation and maybe labelled diagrams
---> consequence for the matter at hand


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PostPosted: Thu Oct 09, 2008 7:07 pm 
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Morning Dove wrote:
And, no offense to Dr. Hanneman, but you don't need a "special" filter for tanzanite ... a regular Chelsea Filter and your dichroscope will do. :)

And none taken. :D
My Tanzanite filter is a tool of "confirmative gemology." It was developed to aid buyers of tanzanite by allowing them to detect blue synthetic forsterite and other man made tanzanite simulants.


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PostPosted: Thu Oct 09, 2008 7:20 pm 
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re: the habit of iolite

it does belong to the orthorhombic system - but you need it's habit:

1 - short (aka stubby) prismatic of rectangular cross-section, the crystal edges rarely sharp

2 - often pseudo-hexagonal in cross-section due to repeated twinning

3 - often massive as spwaue has mentioned

good luck with your exams :)

agfa

ps: let me know if you need refs for above info


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PostPosted: Thu Oct 09, 2008 7:26 pm 
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Actually, Dr. Hanneman, I own your Tanzanite Filter :D and find it handy. It's good for more than just tanzanite. But if money is tight, it's good for newbies to know they don't have to buy every item on the market for gem ID.

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Last edited by Barbara O. Ellis on Thu Oct 09, 2008 10:38 pm, edited 1 time in total.

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PostPosted: Thu Oct 09, 2008 9:13 pm 
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Some garnet crystals may indeed be striated, for example spessartine. I saw one found in a pegmatite in Oxford County, Maine that looked like an old 78 rpm record! The grooves lined up with the edges of a rhombic dodecahedron, so it made a very striking pattern.

Some spessartines from San Diego County, CA and Amelia County VA look like they have been etched to the point of being skeletal. (From photos; I haven't actually held them in my hand.)

Dick Davies


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