Locality: Rt. 16 construction site, Bartlett NH
Specimen Size: 6.5 cm specimen
Field Collected: Tom Mortimer (2008)
Catalog No.: 1653
Notes: Identification by EDS analysis:
Na (1.04 KeV) = 57; Mg (1.24) = 425; Al (1.49) = 602; Si (1.74) = 1641; Mn (5.90) = 43; Fe (6.40) = 357; Background 2KeV/10KeV = 51/9
Analyst stated: "Amphibole with Si/Al ~ 6/2. Negligable Alkalis. Mg dominant."
"My best guess is an intermediate GEDRITE-CUMMINGTONITE on the Gedrite side of things."
[tm notes]
Cummingtonite contains no aluminum and this specimen showed a moderate aluminum content.
Gedrite: [Mg2][Mg3Al2][(OH)2|Al2Si6O22]
Cummingtonite: Mg7Si8O22(OH)2
Gedrite normalized Si:Mg ratio: (6:5) => 1 : 0.83
Cummingtonite normalized Si:Mg ratio: (8:7) => 1 : 0.86
This specimen normalized Si:Mg ratio: 1 : 0.76 (with approximated correction for EDS detector low element response and for Xray relative spectral emission efficiencies.)
Locality: Moat Mtn., Bartlett, NH
Specimen Size: 1 cm field of view. Gray-green ferrogedrite needles on microcline
Field Collected: Art Smith, ex. Bob Janules
Catalog No.: u1404
Notes: Excalibur Minerals EDS analysis performed for Art Smith. Analysis stated: "an amphibole group mineral, close in composition to ferrogedrite. It lacks essential calcium and magnesium for either actinolite or tremolite."
Locality: South of Soapstone Quarry, Richmond, NH
Specimen Size: 3 cm specimen. Weathered gedrite in quartz.
Field Collected: Tom Mortimer
Catalog No.: 1418
Notes: This specimen was previously thought to be anthophyllite. A 2013 EDS analysis of a similar specimen indicated the species was gedrite, (see gedrite page). This specimen was (erroneously) in the New Hampshire species display for several years as the anthophyllite example.
Locality: Soapstone Quarry, Richmond, NH
Specimen Size: 3.7 cm specimen with dark-brown blades of gedrite in quartz
Field Collected: Tom Mortimer - 2013
Catalog No.: 1556
Notes: Gedrite confirmed by EDS analysis .
Locality: Lovejoy Pit Passaconaway, NH
Specimen Size: 9 mm fov. Fibers of ferro-gedrite on albite. Second view about 3 mm
Field Collected: Unknown - circa 1960's
Catalog No.: A Bob Janules specimen
Notes: These fine needles have the appearance of actinolite var. byssolite. Similar material from Moat Mountain has been analyzed to be ferro-gedrite.
Locality: Westmoreland Crushed Stone Quarry, Westmoreland, NH
Specimen Size: 3.8 cm specimen with green blades of gedrite-anthophyllite
Field Collected: Tom Mortimer (1980's)
Catalog No.: 861
Notes: EDS analyzed: Spectrum amplitudes -> Mg = 129, Al = 197, Si = 1043, Fe = 214
Locality: Franconia, NH
Specimen Size: 5.7 cm specimen with black-green blades of magnesiogedrite and almandine (analyzed) garnet. Zoom view 10 mm.
Field Collected: Joey Vaughan - 1/31/17
Catalog No.: 2027
Notes: An EDS analysis (BC170) indicates these black-green blades are magnesiogedrite. Magnesiogedrite (previously a distinct species) is now classified as a variety of gedrite.
Magnesiogedrite chemistry (webmineral) is: Mg3Fe+22Al2(Si6Al2O22)(OH)2
The RUFF data base provides a "measured chemistry" for gedrite of:
(vacant0.61Na0.39)(Mg4.55Fe2+1.40Al0.91Ti0.07Ca0.07)(Si6.56Al1.44)O22(OH)2
The analysis suggests a chemistry (normalized for 2 Al): Mg2.68Fe2.12Al2Si3.22O28
Some comments on these three chemistries:
Webmineral Fe + Mg = 5, RUFF Mg + Fe = 5.95, Franconia Fe + Mg = 4.8. All somewhat close.
Webmineral Al = 4, RUFF Al = 2.35, Franconia Al = 2. RUFF & webmineral very different
Webmineral Si = 6, RUFF Si= 6.56, Franconia Si = 3.22. Franconia very low
Locality: Franconia, NH
Specimen Size: 2.4 cm specimen
Field Collected: Joey Vaughan
Catalog No.: 2099
Notes: Identification by comparison to other Franconia, NH magnesiogedrite specimens.
Locality: Gilsum Road ledge, Surry, NH
Specimen Size: 6 cm specimen with glassy, dark gray-brown, gedrite blades in pale-blue cordierite. Minor pyrite is also present.
Field Collected: Tom Mortimer
Catalog No.: 1614
Notes: Gedrite in cordierite is reported from this site. A polished grain EDS analysis of a sample from this specimen (BC316) gave an APFU calculation of: (Mg5.12,Fe2.28,Ca0.54)Al3.08Si6.0O24.52 , normalized for 6 Si. With Mg >> than Fe, earlier literature would have identified this as magnesio gedrite. Now the IMA identifies Mg rich gedrite as simply gedrite. Note, the presence of aluminum differentiates gedrite from anthophyllite, (also present at this site).
Mindat.org gives a gedrite chemistry as: [ ]{Mg2}{Mg3Al2}(Al2Si6O22)(OH)2 and reports that calcium is a common impurity in some gedrite. Of coarse, an EDS analysis has no way of suggesting how to assign elements to the various parenthesis groups. Additionally, Mindat.org gives a ferro-gedrite chemistry as: [ ]{Fe2}{Fe3Al2}(Al2Si6O22)(OH)2 . American Mineralogist article "Nomenclature of the amphibole supergroup", Volume 97, pages 2031–2048, 2012, states the [ ] = "A" may be filled by Na, K, Ca, Pb, Li, based on a general formula for the amphibole-supergroup minerals as AB2C5T8O22W2 .