On aluminous and edenitic hornblendes

Abstract

SUMMARY. Based on nearly I5oo published amphibole analyses the maximum possible A1 vi in hornblendes is shown to increase with increase of A1 iV. New analyses of hornblendes from amphibolecorundum rocks, with and without anorthite, are given and after critical examination of the available data it is concluded that the maximum verified AlVi-rich calciferous amphibole that approaches the closest to hypothetical tschermakite comes from a kyanite-bearing aluminous high-pressure-crystallized schist from Lukmanier, Switzerland. Pure natural edenite or ferroedenite is unknown, but a new analysis of the nearest known natural edenite, from Mysore, India, agrees with the postulated view that extraordinarily low temperatures are needed for edenite-ferroedenite crystallization, much below that possible in magmas and only rarely achieved in metamorphic rocks containing amphiboles. The limit of the approach of igneous hornblendes to edenite-ferroedenite and tremolite-ferroactinolite is outlined.At least I IOO eC is required for complete expulsion of water from some amphiboles. Aluminous hornblendesA FEW years ago, after examining 936 published amphibole analyses, Leake (I965) suggested that the maximum possible AF i in calciferous and subcalciferous amphiboles increases regularly as A1 i~ increases, where calciferous amphiboles are defined as possessing Ca > I-5O in the half unit cell and subcalciferous amphiboles have Ca between I.OO and 1.5 O. A number of amphiboles that appeared to contain more than the suggested maximum A1 iv for their A1 iv values were re-analysed and the previous values were shown to be erroneous. At that time samples of rocks containing hornblende with either corundum or kyanite were not available to the writer and the line limiting the maximum possible A1 vi was perspicaciously extrapolated to values close to Si 6.00, A1 i~ 2.oo, AF t I-4 o, mainly based on the re-analysis of an amphibole from an anorthite-vesuvianite rock. If this extrapolation is confirmed, then the above value would be the nearest that natural amphiboles approach to the hypothetical pure tschermakite Ca2MgaA12Si6A12(OH)zO2z, which contains 2.oo A1 vi. Recently, Kostyuk and Sobolev (I969, p. 79) have claimed that 55o chemical analyses of amphiboles 'reveal a negative correlation between A1 iv and A1 vi, 'in contrast to the data of Leake 0965)'. However, Saxena and Ekstrom (r97o) using the data given by Leake (I968a) have shown a positive correlation of A1 iv with A1 vi.

Mineral composition of mafic minerals and ore deposition from the Kassiteres (Sappes) and Pagoni Rachi ( Kirki) porphyry Cu-Mo prospects / W. Thrace

“…Πιστεύεται ότι οι περισσότεροι αμφίβολοι των Κασσίτερων δεν είναι πρωτογενείς μαγματικοί αλλά σχηματίσθηκαν στα τελευταία μαγματικά στάδια παρουσία μιας ρευστής φάσης σαν προϊόντα αντίδρα σης της φάσης αυτής με τους κλινοπυρόξενους. Σύμφωνα με τους Leake (1971), Chivas (1981) αμφίβολοι με Si > 7,3 σχηματίζονται κάτω από subsoidus συνθήκες παρουσία μιας ρευστής φάσης. Αντίθετα οι ιδιόμορφοι κρύσταλλοι του δακιτικού ανδεσίτη της Παγώνης Ράχης χαρακτηρίζονται σαν μαγνησιούχοι αμφίβολοι.…”

Nature and physicochemical conditions of crystallization in the South Dehgolan intrusion, NW Iran: mineral-chemical evidence

“…A plot of the Si versus Mg/(Mg + Fe 2+ ) site and most of the amphiboles of the monzogabbro-monzosyenite and syenite rocks are magnesiohornblende to actinolite ( Figure 6). Actinolitic hornblende and actinolite probably recrystallized as a subsolidus phase, since it falls outside the limits of igneous hornblende crystallization (Leake, 1971). Leake (1978) also suggested that amphiboles with Si > 7.3 are considered not to be magmatic, but rather a product of subsolidus reactions in the presence of an exsolved fluid (e.g., Chivas, 1981;Hendry et al, 1985;Agemar et al, 1999).…”

“…In addition, hornblende should have crystallized at approximately the same temperature close to the isothermal solidus and is not applicable to actinolite and actinolitic hornblende (Leake, 1971). Therefore, we have selected hornblende rims without actinolite and actinolitic hornblende compositions for this study (Figure 8a).…”

Constraints on the depth of generation and emplacement of a magmatic epidote‐bearing quartz diorite pluton in the Coast Plutonic Complex, British Columbia

“…Amphibole compositions are ferropargasite-pargasite and ferrotchermakite-tchermakite (Table 3; Leake et al, 2004). The composition of the amphibole suggests that it is igneous (Si £ 7.5 Leake, 1971; also Ca ‡ 1. 6 Hammarstrom and Zen, 1986).…”