| Journal of Pegmatology |
VOLUME 1, NUMBER
1
|
Fluorapatite from the Emmons pegmatite, Oxford county, Maine
Brian
Giller1, William B. Simmons1, Alexander U. Falster1,
Raymond Sprague2, Tony Wielkiewicz2
1Dept. of Geology and Geophysics, University of New Orleans,
New Orleans, LA 70148
2Main Street #9, Andover, MA 01810
Olive-green, blue, lilac, white, and colorless fluorapatites occur within
beryl casts as well a on cleavelandite in miarolitic cavities. A
correlation between crystal morphology and color has been observed.
Olive-green crystals tend to form simple elongate or stubby prisms with
pinacoids. Blue crystals have similar morphology, but shorter aspect
ratios.
Colorless crystals tend to be more tabular with modifications by the dipyramids and other forms. Purple and lilac fluorapatites tend to occur as more complex, almost equidimensional crystals with short prismatic or thick tabular morphology.
Fluorapatites
from the Emmons pegmatite may show very complex and beautiful zoning patterns
with oscillatory zones, chaotic zoning, as well as areas exhibiting partial
dissolution with later overgrowth.
All fluorapatites analyzed are close to end-member fluorapatite, Ca5(PO4)3F
with a wide range of Mn and Sr impurities. The highest observed
content of SrO exceeds 20 wt%.
Generally, however, SrO contents range from 0 to several wt%. No consistent relationship between color hue and minor element content of chromophoric ions such as Mn and Fe was found. Evidently other factors, such as structural defects, are probably responsible for the beautiful colors of these fluorapatites. The widespread, and in some cases, the high Sr content of these fluorapatites indicates a significant Sr content in the parental pegmatitic melts.