Locality: Water Pocket, Blackberry Crossing, Albany, NH
Specimen Size: 4 mm field of view
Field Collected: Tom Mortimer
Catalog No.: u2114
Notes: Macaulayite visual identification by similarity to analyzed macaulayite from the nearby Moose Pocket. A confirming analysis is needed. Samples similar to this are readily available in the tailings of the Water Pocket as coatings on pocket feldspar surfaces and quartz crystal shards. Macaulayite is a rare mineral.
Macaulayite chemistry is: (Fe,Al)24Si4O43(OH)2
A November 2017 polished grain EDS analysis (BC233) gave a chemistry of Fe2.29,Al2.92Si4O59.6 , normalized for 4 atoms of silicon. The Fe + Al content is clearly very low with respect to the Si to be Macaulayite. However, this BC233 EDS plot compares favorably to the three analysis plots of the Moose Pocket macaulayite. See Moose Pocket analyses. I believe the first NH macaulayite identification originated from the Eugene Foord analysis, the second (U.S.G.S plot) of the three Moose Pocket analyses.
A search of IMA approved minerals that must contain Fe, Si, O, H and may allow Al & K yields 32 possibilities, including macaulayite. A powder XRD analysis is needed here.