Patrick,

Some minerals are photoluminescent, fluorescent, or phosphorescent
materials, and silicon dioxide in certain form with proper impurity could be
one of these.  Try to heat the sand to 1000 C and cool down to room
temperature to check again. 

Jingsong    

-----Original Message-----
From: Confocal Microscopy List [mailto:[log in to unmask]] On
Behalf Of Patrick Van Oostveldt
Sent: Wednesday, May 27, 2009 9:30 AM
To: [log in to unmask]
Subject: fluorescent coating

Dear,

We have a user visualizing sand grains, which are suspected to be  
coated with organic material. The grains are suspended in immersion  
oil and become nearly transparent.
The surface can be visualize by fluorescence excitation at 488.
The strange thing however is that heating these samples to 450 celcius  
only partially destroys the original fluorescence.
Is there a mineralogist with can provide a reasonable explanation for this?

Thanks

Patrick Van Oostveldt
-- 
Dep. Moleculaire Biotechnologie
Coupure links 653
B 9000 GENT

tel 09 264 5969
fax 09 264 6219