Cathodoluminescence Colours of α-Quartz

Abstract

A new cathodoluminescence-microscope has been developed with a considerably improved detection limit. Time-dependent luminescence intensity changes observed during electron bombardment enabled the recognition of short-lived, long-lived, and brown luminescence colour types in ~-quartz.Short-rived bottle-green or blue luminescence colours with zones of non-luminescing bands are very common in authigenic quartz overgrowths, fracture fillings or idiomorphic vein crystals. Dark brown, short-lived yellow or pink colours are often found in quartz replacing sulphate minerals. Quartz from tectonically active regions commonly exhibits a brown luminescence colour. A red luminescence colour is typical for quartz crystallized close to a volcanic dyke or sill.The causes of these different and previously poorly understood luminescence colours were investigated using heat treatment, electron bombardment and electrodiffusion. Both natural and induced brown luminescence colours reflect the presence of lattice defects (nonbonding Si-O) due to twinning, mechanical deformation, particle bombardment or extremely rapid growth. The bottle-green and blue linearly polarized luminescence colour, characterized by a plane of polarization parallel to the c-axis, both depend on the presence of interstitial cations. The yellow and red luminescence colours in ~-quartz both exhibit a plane of polarization perpendicular to the c-axis and appear to be related to the presence of trace elements in an oxidizing solution and to ferric iron respectively.

Cathodoluminescence characteristics of Archean volcanogenic massive sulfide related quartz: Noranda, Ben Nevis and Matagami districts, Abitibi Subprovince, Canada

“…Additional images were taken after 1 to 3 min of electron irradiation to reveal any changes in the CL. Through this technique, it was possible to document the transient blue CL which is a characteristic feature of hydrothermal quartz [Ramseyer et al, 1988;Ramseyer and Mullis, 1990;Perny et al, 1992;Götze et al, 2001]. …”

“…This type of transient CL response is characteristic of hydrothermal quartz [Ramseyer et al, 1988;Götze, 1996] and is attributed to (1) and Mullis [1990], Perny et al [1992]), and (2) photon emission associated with the recombination of electrons in the nonbridging oxygen band-gap state [Siegel and Marrone, 1981]. Silanol groups may be the precursor of this second type of emission center in hydrothermal quartz, which is characterized by orange to red CL (620-650 nm).…”

The nature of “quartz eyes” hosted by dykes associated with Au-Bi-As-Cu, Mo-Cu, and Base-metal-Au-Ag mineral occurrences in the Mountain Freegold region (Dawson Range), Yukon, Canada

“…If quartz with brown or red CL response is typical of quartz from metamorphic rocks (Zinkernagel 1978;Ramseyer et al 1988;Boggs et al 2002), the reddish brown luminescent fluid migration trails observed suggest that some "quartz eyes" underwent retrograde metamorphic fluid reaction. But the reddish-brown and reddish CL colours can also be explained by lattice defects induced by twinning, mechanical deformation, or rapid growth (Ramseyer et al 1988).…”

“…The defects causing different CL emissions often reflect the specific physico-chemical conditions of crystal growth and therefore can be used to investigate genetic conditions. Then, according to classification schemes relating the quartz CL colour to the genetic environment (Zinkernagel 1978;Ramseyer et al 1988), the mostly bright bluish and rarely red colours observed suggest "quartz eyes" have a phenocrystic origin (i.e., similar to quartz crystals in volcanic rocks). Likewise the stable luminescence behaviour exhibited by all quartz crystals is indicative of crystallization at higher temperatures, i.e.…”

Fluid-rock interaction processes in the Te Kopia geothermal field (New Zealand) revealed by SEM-CL imaging

“…Mineral non-stoichiometry, poor crystallographic ordering, lattice defects and the incorporation of trace elements into a crystal structure can generate cathodoluminescence ("CL") of varying wavelengths and intensity, which is useful for interpreting a variety of geological phenomena (Marshall, 1988;Ramseyer et al, 1988;Trukhin, 1994;Götze et al, 2001), including the nature of quartz depositional processes (water-rock interaction) in active geothermal settings (Bignall et al, 2004). CL is caused by the emission of photons in response to electron bombardment, and can be observed using a scanning electron microscope (SEM) equipped with a CL detector.…”