The "exact" rock determination based solely on an analysis table and some photo-micrographs (without any scale-bars) is simply impossible.

The following information and/or parameters are required:

Colour

Macro / micro-structure, texture, pattern (grain size, grain shape, grain distribution), orientation of the minerals, distribution of the minerals (homogeneous, inhomogeneous), degree of space filling, etc.

Mineral content (main, medium and accessory components)

Chemical composition

Technical Properties

Best regards,

Guenter Grundmann

name this rock is granit

Grano syenite

I agree it might be grano-syenite, but without 15-20% of iron oxides. As it seems to me the rock similar to some kind of pegmatite (vein derivatives of grano-syenite)

the 15-20% of isotropic brown colored mass of altered by Fe oxides is probbly ,results of biotite or amphybol alteration. that so mineral,s are usual in granocyenite.

altered syenite

The rock abundant with K-spars and low quartz is syenite. Muscovite syenites are relatevily rare, probably formed in exocontact or alteration zone

it is probably a granite

Dear Mirian: the rock accordino to the usual Q-A-P classification in is a syenite to quartz-syenite, the isotropic, actually opaque masses of oxides are altered mafics, perhaps hornblende or biotite, or even egirine... maybe you can find other samples with remains of these mafics to make sure. It certainly contains no glass, so it is a plutonic rock.

Regards, Sebastián

The rock cannot be termed a Granite as the Quartz content is very low. Thus I agree with Sebastian Grande. The rock can be termed as quartz-syenite. The presence of large amount hematitic/limonitic matter is quite unusual.

If you have confirmed this is an igneous rocks then you should be using the IUGS classification of Le Maitre Article Igneous Rocks: A Classification and Glossary of Terms

best wishes

Jana

The rock is intrusive igneous rock as it is coarsely-textured. Since it contains high amount of alkaline k-feldspar (usually orthoclase) but low amount of quartz, relatively low amount of palgioclase and opaque oxides (might be altered ferromagnesium mafic minerals), the rock can't be granite but it can be syenite which is usually deficient in quartz and produced due to partial melting of granitic igneous rock at low degrees of melting at an altering zone such as a subduction zone.

No idea

Dear Mirian: don't get confused, simply apply strictly the I.U.G.S. Igneous Rock Classification, and use the QAP triangle to plot your rock. I've done it, but the result depends on the amount of plagioclase An > 5%. Since you put albite plagioclase together with the more calcic one, you should substract this amount of albite and add it to the percentage of K-Feldspar, since both constitute the "A" parameter of the QAP triangle: alkali feldspar. The "P" parameter is plagioclase with An > 5%, so albite is not considered in it. The rest is quartz, opaques, which could be altered mafics too, and are grouped under Color Index (C.I.), and muscovite, which is not taken into account, but it could indicate a peraluminous granitoid, according to Shand´s ASI index... Assuming that of the 15% total plagioclase you have, some 5% is albite, the parameters come out to be: Q' = 3.5, P = 10, A = 65, C.I. = 15. , which recalculated to fit into the triangular diagram result in: Q = 4,5 ; A = 82,8; P = 12,7, which falls in the field "syenite" (close to quartz-syenite), which has a normal range of C.I. between 10-35, so the definitive name is SYENITE. And usually these rocks are typical of intraplate plutonism, they're not associated to subduction zones. Also, try to find better samples and see what mafic minerals are contained, usually the syenites and quartz-syenite which I have studied here in Venezuela have egirine or egirine-augite (zoned) as mafic mineral, and if the "muscovite" you mention (of which I don't really see too much in the photomicrographs you adjoined) is mostly sericite, it is not a primary igneous mineral, but simply a product of plagioclase hydrothermal alteration, so the rock could be peralkaline to metaluminous. With the chemical table you adjoined I've calculated the ASI index and it the rock has coordinates: A/NK = 1.09; A/CNK = 0.74, which falls in the METALUMINOUS field, but quite close to the PERALKALINE field (which needs A/NK < 1). The total of alkalis in your syenite is about 12%, that's much more than in an ordinary orogenic granite, If you say it is associated to a subduction zone, then it could be part of a back-arc expansion extensional basin, which are also characterized by alkaline magmatism, especially if they are intracontinental. Also, the K-feldspar you have is absolutely microcline, the typical tartan twinning is easy seen in the photos. The altered mafic is really hard to precise, but it could be hornblende or perhaps, egirine.

Kind regards, Sebastián.

Sebastián Grande Mr. Sebastian, I'd like to express my respect and say thank you very much for this interesting and useful answer!

Dear Mirian: there's not much else to say, the rok is a syenite, but the mafics are very altered and impossible to identify. I've studied a similar rock in Central Venezuela, and most of the samples show totally oxydized mafics, but in two of them egirine, with its typical green pleochroism and low extinction angle, has been duly preserved. So, I sugggest you look for other samples of this rock and try to find some which have unaltered mafic minerals, if it was quite possible to do so in tropical environment, it would be a lot easier in an arid climate. It would be the only way to ascertain the presence of hornblende and/or biotite or egirine, or some other Na-rich amphibole, perhaps. Regards, Sebastián.

I fully agree with the arguments given by Sebastian, and the rock seems to be only syenite and not granite.

Advised not to be confused any more on this issue.

I agree that is rock is altered syenite but it is difficult to say that the high amount of opaques is related to alteration of ferromagnesim minerals. May be these patches are geothite filling cracks

This rock contains hornblende and granite

isotropic structure.

Syenite