New Mineral Named After GIA’s John Koivula
Welcome to the GemologyOnline.com Forum
A non-profit Forum for the exchange of gemological ideas
It is currently Sun Oct 20, 2019 12:22 pm

All times are UTC - 4 hours




Post new topic Reply to topic  [ 12 posts ] 
Author Message
 Post subject: Warning: misrepresented inclusions in quartz
PostPosted: Sat Jan 11, 2014 5:07 pm 
Offline
Gold Member

Joined: Sun Jun 28, 2009 9:56 am
Posts: 1221
Some misidentifications of quartz inclusions have largely spread in the gem&mineral market for a long time, so let's clarify a few things:

Known misrepresentations (discredited by lab analysis, sources: Photoatlas vol.1 and vol.2, and the book Inclusions in Quartz):
-cacoxenite inclusions are actually goethite inclusions
-lepidocrocite inclusions are actually hematite inclusions
-hedenbergite inclusions in green prasem quartz are actually mostly actinolitic amphibole inclusions

By the way, I'm wondering about so-called celadonite inclusions in quartz from madagascar, considering that these could possibly be some other kind of green mica group mineral (maybe a variety of phlogopite or muscovite?), or even some chlorite group mineral (maybe clinochlore or chamosite?). Was any analysis ever performed to confirm celadonite inclusions in quartz from madagascar?

ps: I had also been wondering whether or not covellite inclusions in quartz from brasil had actually been positively identified as such through lab analysis, but I eventually found a Gia lab report confirming the identification.


Top
 Profile  
Reply with quote  
 Post subject: Re: Warning: misrepresented inclusions in quartz
PostPosted: Wed Apr 23, 2014 11:30 am 
Offline
Established Member

Joined: Wed Apr 16, 2014 1:46 pm
Posts: 11
Hi !
regarding the classification of inclusions... I always struggle to make sense of the descriptions of inclusions and wondered what your thoughts are about how to properly describe them.
Taking Hematite in Quartz as an example, do you think there is some leeway for wider definition of different forms or habit of Hematite?
Hematite can take a number of forms as an inclusion. It may appear as platelets or the "streamers" usually refered to as Lepidocrocite or Lepidocrosite.
I believe it might be acceptable to differentiate between different habits of a single substance, in the same way that both a Chihuahua and a Great Dane are both broadly categorised as dogs but are unlikely to be confused for each other.
Is it then fair to say that terms like Lepidocrocite or Cacoxenite, which as you quite rightly point out are commercial names, do nevertheless perform a necessary descriptive function?

As for Celadonite, I purchased a Madagascan specimen a few years ago. On inspection the inclusions appear to be very similar to Chlorite phantoms. Just an opinion... look forward to yours :)


Top
 Profile  
Reply with quote  
 Post subject: Re: Warning: misrepresented inclusions in quartz
PostPosted: Fri Apr 25, 2014 10:36 am 
Offline
Gold Member

Joined: Sun Jun 28, 2009 9:56 am
Posts: 1221
Quote:
Is it then fair to say that terms like Lepidocrocite or Cacoxenite, which as you quite rightly point out are commercial names

precisely not, lepidocrocite and cacoxenite are individual minerals, not commercial names for specific habits of goetite and hematite.

Lepidocrocite and cacoxenite have never been positively identified as inclusions in quartz. Every time analysis were performed, only hematite or goethite were detected.

The problem all started with a misidentification, which was printed somewhere, and unfortunately this misinformation propagated to the point that many collectors and merchants are now thinking these are synonyms or varietal names while these are actually completely different minerals! (which is why I felt it was time to create a topic to set the record straight)

Let's put it in a more obvious way:
Goethite and lepidocrocite are polymorphous orthorhombic hydroxide minerals, hematite is a trigonal oxide mineral, and cacoxenite is an hexagonal phosphate mineral: they have nothing in common (besides the fact that they might sometimes share a similar appearence)

note: concerning goethite and lepidocrocite, they are polymorphs (just like rutile and anatase): they share the same chemistry but have different crystallographic structure, thus they are actually two distinct minerals.
The funny thing is that most often, it isn't goethite inclusions which are erroneously labelled as lepidocrocite, but hematite inclusions: not even close!

Concerning celadonite, I couldn't locate any analysis record to prove its existance as inclusions in quartz, so there's a possibility that it is one more misidentification.


Top
 Profile  
Reply with quote  
 Post subject: Re: Warning: misrepresented inclusions in quartz
PostPosted: Fri Apr 25, 2014 3:10 pm 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 3398
Location: North Carolina
I think saying they have nothing in common is a stretch. Goethite is essentially rusted hematite. Cacoxenite is also largely iron oxide and water with a phosphate stuck in the middle. The ingredients are assembled very differently but it's mostly the same stuff. Some instruments (SEM in particular) have trouble picking up low atomic number elements like hydrogen so sorting out hydroxides can be a pain on them--there are ways that cursory tests could have been done and misinterpreted. They pick up phosphorous just fine, though, so there's not much of an excuse on that one.

_________________
https://www.etsy.com/shop/angryturtle


Top
 Profile  
Reply with quote  
 Post subject: Re: Warning: misrepresented inclusions in quartz
PostPosted: Fri Apr 25, 2014 3:58 pm 
Offline
Gemology Online Veteran
User avatar

Joined: Sun Oct 04, 2009 11:18 am
Posts: 595
Location: Madrid, Spain
I totally agree with Cascailou, these are clear misrepresentations, you can't use the name of other mineral to describe morphology or crystal habit.

Diamond and graphite are also same atoms arranged in different way, but they are quite a different stuff... :D I mean, minerals are defined by chemical composition and crystal structure, so we can't misname minerals only because SEM isn't enough to identify them. Just say you don't know or go for other analytical methods!..

_________________
http://gem-sphalerite.com
http://gems-inclusions.com


Top
 Profile  
Reply with quote  
 Post subject: Re: Warning: misrepresented inclusions in quartz
PostPosted: Fri Apr 25, 2014 6:16 pm 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 3398
Location: North Carolina
I'm not saying it's right, I'm just trying to make a guess at how the misidentifications came to be. I would prefer to think it was a simple mistake rather than someone fraudulently trying to make the quartz sound sexier. Though given some things we see in the trade ("azeztulite"... :? ) I am probably being too generous.

_________________
https://www.etsy.com/shop/angryturtle


Top
 Profile  
Reply with quote  
 Post subject: Re: Warning: misrepresented inclusions in quartz
PostPosted: Thu May 08, 2014 1:09 am 
Offline
Established Member

Joined: Wed Apr 16, 2014 1:46 pm
Posts: 11
Thanks for clearing that up for me Cascaillou , and to everyone else who commented.
I didn't realise that Cacoxenite and Lepidocrosite were distinct minerals and so of course it would be misrepresentative to refer to Goethite and Hematite inclusions in Quartz by those names.
That leaves me in a quandary though. Would anyone like to suggest a more accurate way of describing differing forms of Hematite. A few examples...

Image
Image 1

Image
Image 2

Image
Image 3


Top
 Profile  
Reply with quote  
 Post subject: Re: Warning: misrepresented inclusions in quartz
PostPosted: Thu May 15, 2014 11:32 am 
Offline
Gold Member

Joined: Sun Jun 28, 2009 9:56 am
Posts: 1221
sure, there are specific words to describe the shapes of minerals

Hematite morphology (source: mindat):
Crystals generally thick to thin tabular {0001}, rarely prismatic [0001] or scalenohedral; also rarely rhombohedral {1011}, producing pseudo-cubic crystals. Often found in sub-parallel growths on {0001} or as rosettes ("iron crosses.") Sometimes in micaceous to platy masses. May be compact columnar or fibrous masses, sometimes radiating, or in reniform masses with a smooth fracture ("kidney ore"), and botryoidal and stalactic. Frequently in earth masses, also granular, friable to compact, concretionary and oolitic.

Goethite morphology (source: mindat):
Prismatic [001] and striated [001]; also flattened into tablets or scales on {010}. Velvety aggregates of capillary crystals to acicular [001] and long prismatic forms often radially grouped. Massive, reniform, botryoidal, stalactitic. Bladed or columnar. Compact or fibrous concretionary nodules. Oolitic.

a few definitions: http://www.webmineral.com/help/Habits.s ... 3TcxIF_tSs


here is what would simply be described as "hematite flakes":
Image

here is what would be described as "stellate hematite" (or "hematite suns")
Image
Let's note that these suns aren't individual crystals but aggregate of crystals (a sun shaped aggregate of acicular crystals radiating from a single point)

and here's what is described as "hematite rosette"
Image

etc...


Top
 Profile  
Reply with quote  
 Post subject: Re: Warning: misrepresented inclusions in quartz
PostPosted: Fri May 16, 2014 3:31 pm 
Offline
Gemology Online Veteran
User avatar

Joined: Wed Aug 24, 2011 11:48 am
Posts: 584
Location: Odenton, Maryland
On a sorta-related note, would you then describe the classic sunstone inclusions (color zones) as "stellate cuprite"?

_________________
--Eric//upcyclist
Silversmith, faceter, tinker, geek
Select Gem LLP
Patuxent Lapidary Guild


Top
 Profile  
Reply with quote  
 Post subject: Re: Warning: misrepresented inclusions in quartz
PostPosted: Sat May 17, 2014 1:46 am 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 3398
Location: North Carolina
There are a lot of included gem feldspars called sunstone. Which type do you mean? If you're talking about Oregon sunstone, that's actually elemental copper rather than cuprite.

_________________
https://www.etsy.com/shop/angryturtle


Top
 Profile  
Reply with quote  
 Post subject: Re: Warning: misrepresented inclusions in quartz
PostPosted: Wed May 21, 2014 9:55 am 
Offline
Gold Member

Joined: Sun Jun 28, 2009 9:56 am
Posts: 1221
upcyclist, here's an illustration of a radiating stellate morphology:
https://www.mtholyoke.edu/courses/mdyar ... rotalc.gif
But you could also simply describe such morphology as "radiating"


Top
 Profile  
Reply with quote  
 Post subject: Re: Warning: misrepresented inclusions in quartz
PostPosted: Wed May 21, 2014 11:26 am 
Offline
Gemology Online Veteran
User avatar

Joined: Sun Oct 04, 2009 11:18 am
Posts: 595
Location: Madrid, Spain
Here is a good list of crystal habits that can help for description of inclusions too (a bit too extensive list IMHO :roll: ): http://www.webmineral.com/help/Habits.s ... 3zE5ihkkUN

_________________
http://gem-sphalerite.com
http://gems-inclusions.com


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 12 posts ] 

All times are UTC - 4 hours


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Gemology Style ported to phpBB3 by Christian Bullock