The Franklin Mine is TL for clinohedrite, hancockite, and hendricksite, but the main feature of this specimen is the datolite. Datolite is, of course, a very common mineral of traprock quarries (etc.). But it is a rare mineral from the Franklin Mine (and never found at the nearby Sterling Mine).
According to Dunn (Franklin and Sterling Hill New Jersey, etc.) “splendid” crystals to 1 cm have been found. But while there are many diagrams (of unspecified size), there are no photos of any size either in Dunn or in Palache’s USGS monograph (#180). Nor will you find many photos of Franklin datolite on Mindat. In fact, most datolite at Franklin is massive or botryoidal, and most crystals are in the 1-2 mm range (per Dunn).
So this has to be considered an exceptional specimen of datolite from Franklin – the freely growing crystals in the main vug reach ca 2.5 mm. There are many other vugs filled with datolite, but mostly these are cleavages. One or two vugs hold crystals with a face or two, but it’s not clear if these are true faces or contact surfaces.
The first pair of photos (FOV 4.3 x 6.9 mm) shows the main datolite crystals.
The next photo (FOV 5.3 x 4.2 mm) is another view of the same vug, and the next pair of photos (FOV ca 20 x 15 mm) is a broader view of the entire main vug. Depending on how one measures, the crystals may be as large as 3 mm.
The sixth photo (FOV 5.9 x 4.3 mm) shows a pair of striated crystals spanning 4.6 mm. But it’s not clear if the striated surfaces are faces or contacts. Also, the purplish (more like brown in the photo) color is similar to that of some clinohedrite. However, these crystals have no UV response and there is some other clinohedrite on the specimen that fluoresces the usual orange under SW UV, albeit not too strongly. But this clinohedrite (shown in the next two photos) seems to be just thin films – not crystals or crystalline masses. The purplish color may be due to what lies below the datolite, which is essentially transparent.
Regarding the UV photo: The UV response of the clinohedrite, while clearly visible, is no match for the willemite. To make the UV photo I had to resort to Photoshop trickery. One photo was made to capture the willemite, another to capture the clinohedrite. In that second photo, most of the willemite came out as a "blowout". The two photos were merged to produce what you see. However, despite the trickery, what one perceives with the human eye is not too far from the way things appear in the photo. Even though the willemite is glaringly bright, the clinohedrite is clearly visible once the eye is dark adapted.
The last two photos show the datolite/hendricksite side and the hancockite/hendricksite side, respectively. (But there are datolite vugs on all sides.)
A stereo view of the full specimen is available on Mindat under minID 0WL-Q39.
This is a heavy beast – 11.2 oz or ca 320 g. That means that shipments outside the USA will be pricey. But the “good” news is that, for the quoted rate, I can ship up to a total of 32 oz (950 g), so if you buy lots of stuff, or have enough patience to wait for another auction, there will likely be no extra postage charge.
For USA customers, I will ship this at the “own box” Priority Mail rate of $8.50, which is good up to a total weight of 16 oz (including packing).
