CL in Support of Interpreting
Gem Deposits
G. E. Harlow1
E. Sahm1,2
J. Hunt1,3
1 American
Museum of Natural History, New York, NY
2
University of Utah, Salt Lake City, UT
3
California Institute of Technology, Pasadena, CA
MVE02-3-1
(SSS)
Instrumentation
• Hitachi S-4700 Field-Emission SEM with
BSE, EDS and a Gatan MonoCL3 detector
& monochromator system (Peltier-cooled
high-sensitivity PMT). The grating is a
low-dispersion (21.6nm / mm slit width),
with peak response (blaze wavelength) at
500nm and useful range of ~200 - 1200 nm.
CL Applications
Cathodoluminescence is an extremely
powerful technique for examining zoning in
minerals and can lead to fundamental
interpretations about how they formed.
Targets in this presentation:
– Jadeitites: jadeite, zircon, grossular?
– Corundum deposits: ruby, sapphire, painite
Guatemalan Jadeitites
 Jadeitites have been interpreted as crystallizations
from aqueous fluids derived from subductions
channels based, in large part, on CL observations.
 In Guatemala there are two distinct serpentinite
mélanges containing jadeitite, North and South of
the Motagua fault.
 How do the CL signatures of the minerals
compare between the two distinct sources.
Phengite
Qtz
Jd-2
Zrn
Omph
Jd-1
Ttn
MVE02-8-6 Phengite Jadeitite, San Jose
SOUTH
Jadeite-phengite rock
Panchromatic
(MVE02-8-6 – SOUTH)
Jadeite
270 nm
UV
Jd-1
Jd-2
SOUTH
480 nm
Blue
Zircon, Secondary Electrons
Jd-2
Zrn
Jd-1
BSE
Zircon Panchromatic
Jadeite-phengite rock
(MVE02-8-6 –SOUTH)
Zircon
500
315
410
240
Panchromatic
315 nm UV
410 nm Blue
505 nm Green
685 nm Red
Zircon in lawsonite-eclogite
Zircon, Panchromatic
(MVE02-6-1 – SOUTH)
490
230
230 nm UV
490 nm Bluegreen
Pmp
Grs
Jd
BSE
Pmp-Grs-Jadeitite
(MVE04-20-1 – SOUTH)
Jadeite
330
940
600
Panchromatic CL
MVE04-20-1 Pmp-Grs-Jadeitite
SOUTH
Panchromatic CL
Jadeite
BSE
Panchromatic CL
MVE04-20-1 Pmp-Grs-Jadeitite
Panchromatic
600 nm Green
Jadeite
300 nm UV
940 nm IR
Pmp
Grs
Jd
BSE
Panchromatic
Pmp-Grs-Jadeitite
(MVE04-20-1 – SOUTH)
Grossular
590
~850
475
335
Panchromatic
NORTH
Jadeitite, Río La Palmilla, North of MFZ
(MVJ84-9D) 2 cm across (courtesy of S. Sorensen)
NORTH
Panchromatic CL image of same area.
Note healed fracture in jadeite grain.
NORTH
Close-up from previous image
NORTH
Altered Jadeite (MVJ84-9B)
at boundary between Jd and Ab+Ne
NORTH
Room Temperature Spectrum Imaging
Scale bar is 1 about micrometer.
Spectrum Image (40 X 40 pixels) of
adjacent area
NORTH
Point 0
Point 1
Nepheline?
Albite?
Darker Jadeite
Lighter Jadeite
Point 3
Room temperature CCD CL spectra
courtesy of Paul Mainwaring
~700
~560
~480
~700
~560
Point 2
Zircon, Meta(?)-Jadeitite
(MVJ84-9C – NORTH)
547
350
279
279 nm UV
350 nm UV
547 nm Green
Jadeite-Phengite rock
(MVE02-8-6 -- SOUTH)
Comparison of CL Spectra
from Jadeite
480
 UV to IR peaks, but too
soon to make
generalizations other than
color zoning observed by
Sorensen and co-workers.
270
Pmp-Grs-Jadeitite
Altered Jadeite
(MVE04-20-1 -- SOUTH)
(MVJ84-9B -- NORTH)
Jadeite
~700
~480
940
600
~560
330
Zircon in lawsonite-eclogite
(MVE02-6-1 -- South)
Comparison of CL spectra
from zircon
490
230
 Main peak near 500nm
and lowest near 250nm,
but …
 All are features show
only primary growth.
Jadeite-phengite rock
Zircon, Meta(?)-Jadeitite
(MVE02-8-6 -- South)
(MVJ84-9C -- North)
Zircon
547
500
350
410
279
315
240
BSE
Ruby (107643), Mogok, Burma in
Marble w/ Spinel, Blue Cancrinite,
Sodalite, Scapolite, Phlogopite, etc.
840
694nm - Cr
320
Panchromatic
320 nm UV
695 nm Cr-ruby
Artifact of mirror
840 nm IR
840 nm IR
Ruby-1, Namya, BSE
Ruby-1, Namya, CL
Ruby-3, Namya, BSE
Ruby-3, Namya, CL
Painite (CaZrBAl9O18)
from Namya, Myanmar –
rare gem mineral
probably grew during
skarn formation  CL
shows fine growth
layering, implying
growth pulses.
Panchromatic
Inclusions: Cc, Baddeleyite
(ZrO2) & Srilankaite (TiZr2O6)
Some Conclusions
CL in zircon, jadeite and garnet of jadeitites
is likely due to REE based on enrichment in
these rocks.
Zoning structures suggest growth from
fluids – for Zircon in jadeitite this implies
growth at T = ~ 300°C at P > 1 GPa.
Considerable spectral structure from UV to
IR is seen via SEM/CL.
Lots more to do.
Many Thanks to:
 Jade & Ruby Helpers: Jinny Sisson, Sorena
Sorensen, Carlos Gonzales, Mauricio Chiquin,
Will Maze, Bill Larson, George Rossman, Jamie
Newman, U Han Htun, Dr. Saw Naung U, Mint
Soe
 The Founders of the Feast: AMNH, NMNH,
Frohlich Charitable Trust, Astor Expedition Fund,
Sprague Fund, Michael Scott, & the National
Science Foundation.