Locality: Colony Mine, Alstead, NH
Specimen Size: Top photo: 11 cm specimen before break-up. Second photo: 1.5 cm crystal extracted from pegmatite chunk. Other photo sizes as annotated.
Field Collected: A purchased specimen from a known friend. Collected 1998.
Catalog No.: 2133
Notes: Crystal (second photo) was dislodged in trim from the six inch pegmatite chunk, top photo. The crystal was restored to the matrix for my collection. The surrounding redish-brown mineral is sphalerite.
At the May 2020 time of this photo, this is the best-formed, cm plus sized, NH columbite crystal photo known to me [tm].
Two micro-boxed columbite crystals were also extracted from the original 5 pound rock, u2369 & u2370, photos included here.
What is interesting, and perhaps significant, is that I can find no instance in mindat's million plus photos of columbite in close association with sphalerite. (and in this Colony Mine case embedded in sphalerite).
Jim Nizamoff opined on seeing these photos: "Columbite is not usually directly associated with sphalerite although it often crystallizes in the same zone or area of a pegmatite. Are you absolutely sure that the matrix is sphalerite? Several pegmatites here in Maine contain similar stuff although I don’t recall them having such a direct association (Estes Q is one). I would expect that several NH pegmatites would be capable of producing similar quality columbite (Turner, Chickering, or Chandler) although I doubt that it would be with a ton of sphalerite."
Ray Meyers, on seeing these photos, recalled that I had already analyzed this columbite and sphalerite. Checking my EDS notebook (logging over 500 analyses) showed Ray was correct. The EDS analysis of the columbite indicated a chemistry of (Fe0.53,Mn0.47)(Nb0.48,Ta0.02)O5.8 . This is close to the midpoint of columbite-(Fe) and columbite-(Mn). The analysis Nb + Ta is low. The APFU was normalized for Fe + Mn = 1. Arrow in the top photo indicates site of analysis grain source.
The sphalerite was also analyzed (addressing Jim's uncertainty). The EDS analysis confirmed sphalerite with moderate iron content Zn0.8Fe0.2S1.15 . Checking sphalerite analyses in Dana's System of Mineralogy (Seventh edition, vol 1) there is a ferroan sphalerite: "dark colored varieties with more than ten per cent Fe." The BC analysis indicated 9.97 atomic % Fe... close enough to the 10% threshold that I will call this ferroan sphalerite.
Locality: Ham-Weeks Mine, Wakefield, NH
Specimen Size: 3.2 cm specimen
Field Collected: Don Swenson
Catalog No.: A Don Swenson specimen
Notes: Specimen gives a weak response on my scintillometer, indicating the presence of some uranium.
Locality: Ham Brook - 1100 ft elevation, Albany, NH
Specimen Size: 0.4 mm star crystal on microcline
Field Collected: Bob Janules - 1996
Catalog No.: A Bob Janules specimen
Notes: These black stars were analyzed by SEM-EDS. Label indicates "SEM# GFHB001".
Locality: N. Sugarloaf Mtn. Bethlehem, NH
Specimen Size: 2.3 cm high specimen.
Field Collected: Gene Bearss
Catalog No.: 2087
Notes: A polished grain EDS analysis BC274, showed an iron dominant niobium mineral. Interesting that the Ta plot peak is much higher than the Nb peak, but the atomic percent (in table) of Nb is much greater than the atomic percent of Ta. This demonstrates the difference between the element abundance ratio implied by the plot and the element atomic percents computed by the EDS instrument software after applying the ZAF and instrument calibration corrections. This is a lesson in "do not read too much into relative peak values."
The APFU calculated from the EDS atomic percents gives: (Fe3.51,Mn0.95)(Nb1.53,Ta0.46)O20.7 , normalized for Nb + Ta = 2. Columbite-(Fe) chemistry is: FeNb2O6 . This Sugarloaf analysis shows about twice as much Fe + Mn as columbite-(Fe) should have. Unsure what to make of this.
Specimen backside has nice micro bertrandite.
Locality: Raymond, NH
Specimen Size: 2.2 cm crystal
Field Collected: W. Johanson - 1943
Catalog No.: 2121
Notes: Perhaps from the Chandler Mine. Undetermined whether columbite-(Fe) or columbite-(Mn).
Locality: N. Sugarloaf Mtn., Bethlehem, NH
Specimen Size: 1.5 mm field of view. Termination end of columbite-tantalite blade.
Field Collected: Tom Mortimer - May, 1989
Catalog No.: u149
Notes: Analysis done for 1990 R&M article indicated a composition intermediate between ferrococombite and ferrotantalite. An EDS analysis of a massive chunk of this showed about a 4:1 ratio of Fe:Mn.
Locality: Parker Mtn. Mine, Strafford, NH
Specimen Size: 0.3 mm crystal
Field Collected: Bob Wilken - 2021
Catalog No.: A Bob Wilken specimen & photo
Notes: Nice photo of a tiny crystal