The following is modified from a letter from Gordon L. Nord, Jr. (USGS)
to the granite-research news group on 11 January 1996.
<pre>
Dear blue-quartz readers,

	In a study on very blue quartz found in the Roseland charnockites of 
central Virginia I found the following in a thin section of quartz that graded 
from blue to white.

	(1) The blue color of the quartz is seen only in reflection and is 
red-brown in transmission.  This is observed by eye looking at a rather thick 
polished thin section in natural light.

	(2) In the petrographic microscope both the blue and white areas contained 
rutile needles.  Also a fine dusting of particles was visible in the blue 
quartz at the highest magnifications.

	(3) The concentration of TiO2 and FeO in the blue quartz as determined by 
the probe was only twice that of background.

	(4) An ATEM study of the blue quartz showed disk-shaped particles 
approximately 100 nm thick and 1 um in diameter.  EDS showed the presence of Fe 
and Ti in the particles.  Selected area diffraction confirmed that the 
particles were ilmenite.

	(5) The density of particles per unit area was less in the white quartz.

The backscattering of blue and the forward scattering of red along with the 
presence of abundant high refractive index particles in the size range of 1/4 
of the wavelength of light confirms "Raleigh Scattering" as the mechanism for 
the blue color in the Roseland Charnockites. 

The Llanite blue quartz has a shiller which results from a common orientation 
of the particles (ilmenite has been suggested) as in moonstones.

An easy test for "Raleigh Scattering" is the reflection/transmission test as in 
blue sky and red sunset.



								Cheers,
								Gordon
Gordon L. Nord Jr.
959 National Center
U. S. Geological Survey
Reston, VA 22092

Office: 703-648-6745
FAX:    703-648-6789

gnord@mactem.er.usgs.gov
</pre>