UV MineralsIs this another Franklin prehnite?
This is another Franklin semi-mystery piece from the Roy Epting, Jr. collection detailed in some earlier posts under fluorescent minerals. The non-fluorescent minerals are the typical andradite/franklinite/hendricksite leaving a buff to white, fine-grained groundmass that appears to be mostly platy grains (not fibrous like xonotlite - ignore the file names, that was based on an initial assumption) and elongated grains with two primary SW fluorescent colors - bright yellow (the elongated grains - apparently wollastonite) and a lavender - with some variation in shade as can be seen in the photos. MW is very weak and dull, but not red like margarosanite, with faint yellow wollastonite. LW nothing. I think the platy grains with lavender, variable fluorescence must be prehnite - not the classic peachy color, but nothing else matches its general appearance and has quite the right SW UV color with no MW color.
It certainly looks right for Franklin Prehnite, assemblage and associated Minerals with the platy nature visible in photo. Size?
Steven 
Right, 12 x 7 x 4 cm, closeup FOV is 3.5 cm. Here is the SW companion to the closeup, could only do 3 attachments to initial post. Note the big area of wollastonite not at first obvious in the daylight photo, those grains are much larger than the lavender fluorescing grains. I know hard to see them in this 2D, but lavender fluorescing grains are very small aggregates of radiating plates. Easier to see in the SW image, some are edge on at upper left juxtaposed with wollastonite.
Also note the variation in color in the full view from grayish lavender at upper right, to purplish to more blue around the wallastonite left of center. These are real variations visible when hand held under the UV light. They dont seem to match at all the prehnite color descriptions, so maybe that should be expanded if this is truly prehnite.
Very nice specimen! The violet fluorescence is prehnite and the orange is pectolite. I had a discussion last May with Earl Verbeek and Dick Bostwick about this particular color response of prehnite.
Peter Thanks. The fluorescent descriptions in the upcoming FrOg book, which include habit and assemblages, are most helpful, along with the other usual sources. But of all the fluorescent things in this collection the prehnites have given the most ID trouble relative to its UV color descriptions. Mostly came down to process of elimination and like others have ended up in these messageboard posts for comment. Yes, I have had same problem as you have noted and in many instances I have had to get analyses done to confirm the identity. Prehnite has a fairly wide range in the color of its fluorescent response. The upcoming book will certainly help in the identification of prehnite fluorescent response and many other species as well.
