The presence of clinopyroxene, hastingsite
, with or without paragsite, characterizes the intermediate zone, while only clinopyroxene with minor arfvedsonite were noted in the periphery.
The rock-types are characterized by alkali feldspar ([Or.sub.32-63]), clinopyroxene ([Wo.sub.43-48][Fs.sub.10-32]), and nepheline ([Ne.sub.85]) and hastingsite
. Common accessories include titanite and apatite [+ or -] carbonate [+ or -] zircon.
The higher [Fe.sup.3+]/[Fe.sup.2+] ratio characteristic of hastingsite
may be suggested from coexisting ferrifassaite or titanomagnetite and according to the charge calculated.
35 (1997), (= hastingsite
) 219 Herschelite (= chabazite-Na) Coombs et al.: Can.
Essential minerals are phenocrysts and glomerocrysts of anorthoclase, sanidine up to 1,5 cm and anorthoclase-mantled plagioclase; accessory minerals are red biotite, and hastingsite while trace minerals are augite, zircon, sphene and magnetite.
Accessory and trace minerals are corroded and oxidized hastingsite (Figure 6), euhedral zircon and euhedral sphene.
In the glassy matrix there were identified finer crystals of anorthoclase, hastingsite, oxihornblende and sphene.
there was no chemical and no physical equilibrium between plagioclase and hastingsite crystals and the melt, as suggested by dissolution texture, reabsortion and reaction borders (Figures 6A, 613, 6E, 14D).
It is interesting to note that analytical data exist in the literature for at least two amphiboles which fall into the hastingsite field and which are chlorine-dominant; one of these is almost completely characterized but the data for the other consists only of chemical analytical data.
[ ] Hastingsite, [Mathematical Expression Omitted], mon., forms a series with Magnesiohastingsite, Amphibole group, Can.
[ ] Magnesiohastingsite, Na[Ca.sub.2]([Mg.sub.4][Fe.sup.3+])[Si.sub.6][Al.sub.2][O.sub.22] [(OH).sub.2], mon., forms a series with Hastingsite, Amphibole group, Can.
These rocks were classified as alkaline rhyolites crystal-vitric tuffs, with aligned sanidine, anorthoclase, hastingsite
and sphene crystals in a glassy matrix (Pardo, 2004).