An
Investigation of Greenish Quartz found at the Thunder Bay Amethyst
Mine Panorama, Thunder Bay, Ontario, Canada, and Similar Localities
Laura B, HEBERT and
George R. ROSSMAN
Division of
Geological and Planetary Sciences, California Institute of Technology
Pasadena,
California 91125-2500, USA
Abstract
Naturally occurring greenish quartz found within the
context of amethyst-bearing deposits is not simply the result of the exposure
of amethyst to thermal bleaching or exposure to the sun. Rather, it can represent
a set of distinct color varieties resulting from the changing chemical and
thermal nature of the precipitating solution. Greenish quartz occurs at the
Thunder Bay Amethyst Mine Panorama (TBAMP), Thunder Bay, Ontario, Canada, in several distinct
varieties. Yellowish green quartz and
dark green quartz with purple hues occur as loose detritus, and pale greenish gray quartz occurs as part of a color-gradational mineralization sequence involving
macrocrystalline quartz of other colors and chalcedony. The TBAMP system contains a number of color
varieties of quartz including greenish, amethyst, colorless, and smoky. Spectroscopic, irradiation and controlled
heating studies show that changes in salinity and temperature of the
hydrothermal system that produced the TBAMP deposit are reflected in the
changing coloration of the quartz. The
greenish quartz, especially the greenish gray variety, has increased turbidity
and fluid inclusions when compared with the adjacent amethyst. Analysis of different colors on major (r = {10-11}) and minor (z = {01-11}) rhombohedral sectors within
the quartz indicates that changes in the growth rate also have influenced color
development. As the system evolved, two
factors contributed to the color changes. A minor ferric component appears to
change position from interstitial to substitutional within specific growth
sectors and the trace element composition of the quartz evolved. The samples from the TBAMP deposit are
compared to isolated samples of greenish quartz collected from three other
amethyst-bearing localities: Farm Kos and and Farm
Rooisand
(Namibia), Kalomo-Mapatiqya (Zambia), and Southern Bahia (Brazil). All included similar greenish hues with the
exception of the yellowish green variety.
Colors within the quartz are consistently correlated with the speciation
of hydrous components. Darker green samples incorporate larger amounts of
molecular water than either pale greenish gray samples, colorless samples, or amethyst. The appearance of strong hydroxyl peaks in
the infrared spectra is limited to amethyst and colorless
The paper appeared in Canadian Mineralogist 46, 111-124.
Additional Information:
Spectacularly green quartz is reported from Coos County, New
Hampshire, USA.
Sun-bleached amethyst from the area between Kalomo and Mapatiqya, Zambia
, turns light green. It can also be produced by heat-treatment.
A gemological report on "greened amethyst"
Canadian Mineralogist, 46, 111-124.
