UVITE Chapter16. Sorosilicates and cyclosilicates

UVITE

(Ca,Na)Mg₃(Al₅Mg)B₃Si₆O₂₇(OH,F)₄Hexagonal




	Figure 16-27. Crystal drawings of uvite from the Fowler Quarry in Franklin. Drawings are from Palache (1935) who provided crystallographic data.

Uvite is by far the most common of the tourmaline species at Franklin. Much of the tourmaline described and figured by Palache (1935) is this species, a mineral of the Franklin Marble. Before the individual species were defined, such material often was called by the general name tourmaline. Uvite was redefined and established by Dunn et al. (1977).

Description

Franklin uvite occurs in euhedral crystals up to 10 cm in dimension; most are equant in habit. The morphology was described in detail by Palache (1935). Typical crystal habits are depicted in figures 16-27 through 16-32. Franklin uvite is light green or light brown for the most part. Where color zoning is evident, it consists mostly of green outer zones on brown or lighter green cores; such outer zones are commonly quite thin, commonly of faint color, and rarely emerald green. The luster is vitreous; cleavage is absent; and the density is 3.05 g/cm³. Optically, it is uniaxial, negative, with w = 1.634 and e = 1.620. The fluorescence in ultraviolet is orange-yellow in shortwave. Uvite, when massive, is differentiated from apatite by its superior hardness.




	Figure 16-28. Crystal drawings of uvite from the Franklin Iron Company Quarry in Franklin. Drawings are from Palache (1935) who provided crystallographic data.		Figure 16-29. Crystal drawing of uvite from Sterling Hill. Drawing is from Palache (1935) who provided crystallographic data.

Composition

Uvite is a calcium magnesium aluminum boron silicate hydroxide mineral of the tourmaline group; sodium may substitute for calcium. Wet chemical analyses of a green Franklin uvite and of a brown uvite from an unknown locality assuredly in the local area are given in Table 9, and 12 microprobe analyses of local uvites were presented by Dunn et al. (1977). These indicate that Franklin uvite is near end-member composition, with limited substitution of Na for Ca, and with FeO less than 2.4 weight percent in all analyses. Boron isotope data for Sterling Hill-sited, marble-hosted uvites were given by Swihart and Moore (1989) and by Palmer and Slack (1989); both studies obtained generally similar values.




	Figure 16-30. Equant uvite crystal in calcite from Franklin. Field of view is approximately 5 cm in maximum dimension. Smithsonian Institution, #C3283-4. Photo by Chip Clark.		Figure 16-31. Superb uvite crystal in calcite from Franklin. Field of view is 10 cm in maximum dimension. Smithsonian Institution, #116455. Photo by Chip Clark.

Occurrence and paragenesis




	Figure 16-32. Sharp, euhedral uvite crystal in calcite from Franklin. Specimen is 7 cm in maximum dimension. Privately owned. Photo by the author.

Franklin uvite occurs in the marble quarries of the area. Palache (1935) reported fine crystals from the Fowler quarry, where they occur in calcite with graphite, and from the Franklin Iron Company Quarry, where they are associated with titanite, arsenopyrite, pyrrhotite, pyrite, fluorite, and other minerals. Numerous crystals fitting Palache’s descriptions were examined by the writer and found to be uvite in each case (Dunn et al., 1977).

Uvite crystals were described by Palache (1935) from the hemimorphite deposit at Sterling Hill; he suggested they were introduced mechanically through weathering of surrounding marble.

Generally, uvite crystals occur isolated in white marble; there are few minerals occurring as associated megacrysts (Figures 16-30, 16-31, and 16-32). As such, the specimens have strong esthetic appeal. Some have been carved in relief from the surrounding calcite (Figure 7-15). Uvite is among the most prized of the minerals found in the Franklin Marble. Many of the best specimens are at Harvard University.

FOOTER LBI




Copyright © 1995 by Pete J. Dunn			Website by Herb Yeates

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