Locality: Hurricane Mtn., Conway, NH
Specimen Size: 12 mm field of view
Field Collected: Tom Mortimer
Catalog No.: 576
Notes: I have wondered for many years if these black hair specimens (I collected many) are arfvedsonite, riebeckite, or perhaps aegirine. All are possibilities from the Hurricane Mtn. locality. A qualitative EDS analysis did not resolve the ambiguity (the sodium response of EDS detector is low and not indicative of the true sodium proportion). Both arfvedsonite and riebeckite have a Fe:Si ratio of 5:8. Aegrine is lower, 4:8 (1:2). The plot appears to support a 5:8 ratio.
A review of two articles in volume 34 of the Canadian Mineralogist indicates this fibrous amphibole is riebeckite:
http://rruff.info/doclib/cm/vol34/CM34_1011.pdf by Foord et. al.: "The fine-grained riebeckite is a product of final low-temperature hydrothermal solutions that were present in the miarolitic cavities."
and
http://rruff.info/doclib/cm/vol34/CM34_1015.pdf by Hawthorne et. al. "fibrous Li-poor riebeckite partly fills some of the miarolitic cavities"
A 16 image stack processed with Helicon Focus.
Locality: Hurricane Mtn., Conway, NH
Specimen Size: 7 cm specimen with large zone of blue riebeckite var crocidolite.
Field Collected: Tom Mortimer (1982)
Catalog No.: 178
Notes:
Locality: Hurricane Mtn., Conway, NH
Specimen Size: 4 cm specimen with zone of blue riebeckite var crocidolite.
Field Collected: Tom Mortimer (1982)
Catalog No.: NC
Notes:
Locality: Hurricane Mtn., Conway, NH
Specimen Size: 2.2 cm specimen with acicular black hairs of riebeckite
Field Collected: Tom Mortimer (1982)
Catalog No.:
Notes:
Locality: North Moat Mtn., Bartlett, NH
Specimen Size: 2 cm mass of fibrous riebeckite
Field Collected: Gene Bearss (1985)
Catalog No.: A Gene Bearss collection specimen
Notes: Identification by Gene Bearss.
Locality: Hurricane Mtn., Conway, NH
Specimen Size: 1.6 cm terminated crystal, front and back views
Field Collected: Unknown - A purchased specimen - 8/15
Catalog No.: 1964
Notes: When purchased, this TN specimen was labeled as arfvedsonite. However the scratched surface is pale blue (visible, second photo), suggesting riebeckite.
An XRD analysis - arfvedsonite correlation had a slightly better correlation with arfvedsonite than with riebeckite XRD analysis - riebeckite correlation . This suggests an arfvedsonite crystal altering to riebeckite.
Locality: Hurricane Mtn., Conway, NH
Specimen Size: 2.2 cm field of view
Field Collected: Leroy Grant -1970's
Catalog No.: u2371
Notes: Mat of blue crocidolite on smoky quartz crystal with astrophyllite..
Locality: Hurricane Mtn. Conway, NH
Specimen Size: 5 cm specimen with blue crocidolite in quartz-feldspar matrix
Field Collected: Leroy Grant -1970's
Catalog No.: 2170
Notes: An EDS analysis (BC502, a weight % oxide analysis) had the required elements for riebeckite, but the Na value was low and the Fe value was high for riebeckite.
Chemistry from BC502 analysis: Na1.01Fe8.13Al0.07Si7.13O23 normalized for 23 O.
Al Falster of the MMGM lab acquired an EDS analysis from this same polished grain. Al's plot amplitudes are similar to the BC analysis, but weight % oxide values were not provided.
For reference:
Ideal riebeckite chemistry (mindat, 2023): [ ]Na2(Fe2+3Fe3+2)Si8O22(OH)2
RUFF empirical chemistry (R050082.2):
([ ]0.63,Na0.19K0.18)(Na1.58Ca0.42)Σ=2Fe2+3.00(Fe3+1.30Fe2+0.45Mn0.15Mg0.05Ti0.05)Σ=2(Si0.98Al0.02)8O22(OH)2
A 1996 Canadian Mineralogist article by Foord et. al. , article link
"Li. AND F.BEARING ALKALI AMPHIBOLE FROM GRANITIC PEGMATITE AT HURRICANE MOUNTAIN, CARROLL COUNTV, NEW HAMPSHIRE"
gave an empirical chemistry for a Hurricane Mtn. fibrous riebeckite as:
(Na1.82K0.05Ca0.01)Σ=1.88(Fe2+2.44Li0.06Mg0.02BeO0.02Mn0.01Z0.06O0.01)Σ=2.56 (Fe3+2.42Ti0.01Zr0.02Sn0.01Nb0.01)Σ=2.56(Si7.85Al0.01P0.01)Σ=7.96O23.2
Good grief !
If all the the tiny cation amounts are removed from this formula, we are left with:
Na1.82(Fe2+2.44Fe3+2.42)Si7.85O23.2 reasonably close to the ideal riebeckite formula given above.