As always, it can be a trial trying to blindly identify from snapshots like this. i cant really see the scale or know the orientation of images to your polarisers etc.

The most clear one is the last picture, which has a morphology which is likely to make it sphene (classic double wedge shape).

The high birefringence images MIGHT be monazite, which should have inclined extinction as well as other properties which can be distinctive with large grains.

I guess the simplest thing is you must have done some analytical work if you know they are REE bearing. What kind of data did you collect and will this help? 

Dear Dilip: it was a great idea you had to send the pictures as a Power Point file, they can easily be unloaded and saved. The first and third are very hard to interpret, because they are seen only under crossed polars, views without crossed polars would be more appropiate to ascertain if they are of allanite, since they could show the typical orange-brownish absortion colors of this species. The second and fourth are undoubtely of titanite or sphene: the typical rhombic and wedge-shaped habit and very high relief are diagnostic, also in the fourth picture faint rhombic cleavage planes can be seen in the top-right part of the crystal. In the second picture, the titanite crystal shows the following features: it looks zoned in the border, being quite evident this zoning in the left and top part of the crystal, so I would recommend a transect from the nucleus of the crystal to its border with a microprobe to see the nature of this zoning, because it could be caused by variations in, precisely, REE, Nb, and/or Sn. Also, this same crystal hosts a rounded, apparently oscillatory zoned zircon inclusion, and some slender acicular prisms of possible apatite. In the fourth picture the lowermost biotites also have lots of tiny inclusions, probably those in the left leaflet are of zircon prisms, as they show faint radioactive haloes, others, more irregular could be of allanite too. Finally, in the possible allanite of the third picture a thin zone of epidote has developed in contact with the microcline crystal, this is visible in the top-right of the crystal as a polychromous band. I would like to see these "allanites" with uncrossed polars, to make sure they are really allanites... With regards, Sebastian.

Dear all, Thanks for valued observations. I am again posting detailed photomicrographs of the minerals I find difficult to make identification although I guess presence of allanite, titanite, apatite, zircon etc.

Regards

D. Majumdar

Dear Dilip: I've been unable to unload the second presentation of photomicrographs you sent, perhaps it is a bit too "heavy", try to split it in three or four different files, the first one had only four pictures and came through with no problem. With this second one I keep receiving the message: "Error, network error"...

Dear Dr. Dilip,

Good day. Due to my experience in identification of REEs-bearing minerals, I believe that the first-three photographs are referred to zircon, whereas the fourth photo refers to sphene,

The second and fourth one are undoubtedly the images of sphene.

the images of one and three can be confirmdly identified once you can give images under one nicol.

I guess those are suggesting the species refer to allanite-(Ce) and titanite are correct.

I presume that the suggestion came from Dr. Sebastian is true to the belief and by now I have had some EPMA results that are helpful for the identification of minerals. Thanks to all those scholars helping me with their valuable suggestions.