Occurrence
Friedelite was first identified among the Franklin minerals by the author (195) on a specimen in the Kemble collection, found by Mr. Kemble many years ago in the Buckwheat mine. The mineral covers a surface of 2 or 3 square inches of massive granular franklinite-willemite ore and is apparently part of one wall of a thin transverse vein. The friedelite, massive beneath the surface and in tiny crystals on it, is largely covered with a botryoidal coating of magnesian. calcite which, in turn, bears on its surface a few platy crystals of barite. The specimen has the appearance of rhodochrosite, for which it was at first mistaken. It is now in the Harvard mineral collection.

Friedelite was also identified in extremely small amounts in two small specimens in the Canfield collection. It had the same form as that already described—flattened crystals, with narrow rhombohedral faces and no evidence of hemimorphism, in that respect being like the friedelite found in Europe.

A remarkable specimen of friedelite, now in the Hancock collection at Harvard University, was found in 1909 in the Taylor mine. The specimen contains a triangular cavity, 1-½ by ½ by ½ inch, shown in plate 14, C. The walls consist of a dark-green slickensided chloritic mineral mixed with magnetite, on which is a lining of more definite crystals, set edgewise, of the same chloritic substance. Within the cavity are white tetrahedrons of sphalerite as much as a quarter of an inch on an edge; rhodochrosite in platy rhombohedrons lines one inner surface and massive granular yellow friedelite another; and upon the massive friedelite and last to form in the cavity are implanted crystals of friedelite, which are sharply hemimorphic, the largest being not quite half an inch in diameter, and each is attached to the wall by the rhombohedral end, with a brilliantly lustrous base as the tipper termination. These crystals are the first on which evidence of hemimorphism had been seen (figure 133).

On a part of the same specimen, belonging to Mr. Gage, tiny crystals of friedelite were completely embedded in barite, from which they were easily removed uninjured. Though rough and striated they yielded the measurements recorded here. One of them is shown in figure 134. A part of the massive friedelite lining this specimen was analyzed by Gage. (See analysis 5.)

Since 1910 numerous specimens of friedelite have been found at Franklin, representing a variety of forms and associations. Fibrous crusts of a dark-red form of the mineral are associated with the fine crystals of tephroite that were found in 1915. (See page 77.) In the Harvard mineral collection there are, besides the specimens already described, one showing films of dark-red friedelite in columnar masses cutting massive garnet with later calcite and willemite, another showing granular yellow friedelite in patches in massive light-green willemite, and another showing a light-yellow crust of crystalline friedelite covering the bases of crystals of green willemite.

Solid veins of compact friedelite as much as 2 inches thick have been found since 1925. In the Stanton collection there were abundant specimens of pale-red friedelite showing thin veins with many cavities, their walls lined with tiny crystals. These specimens came from the 200-foot level south in the footwall pillar 854.

Analysis 4 in the table was made on this material. The crystals are similar to those of figure 134 but lack the positive rhombohedron q. Calcite and barite are the only associated minerals in these veins.

In another group of specimens veins of compact brown friedelite have open spaces whose walls are covered with light-yellow crystalline crusts. Although not measurable, the slender needles are clearly hemimorphic and are well represented by figure 135, except that they appear more slender. With them are the hematite crystals described on page 42.

At Sterling Hill friedelite has also been found forming veins and stringers and mixed with calcite, cutting the massive ore. It is of lively pink color and is mostly compact but with scattered drusy cavities. A specimen from the 1,300-foot level, stope 720, with a specific gravity of 3.014, was analyzed by Mr. Bauer. Although it differs somewhat in composition from the other analyzed material in its high magnesia and alumina, it is undoubtedly to be regarded as a low chlorine friedelite.