Mineralogy mid Geology. 485 



to (100) and somewhat elongated parallel to b axis. Dimensions 

 2 mm. by 1mm. Other forms, rarely observed, are (110), (001), 

 (101). Measured under microscope gave approximate angles ; 

 (100) :(110) = 32° 50', (001) :(100) = 61° 5' (101) :(100) = 56° 50'. 

 Axes « : Z> : c = 0'74 : 1 : 0*84; /? — 61° 5'. Cleavage good prob- 

 ably parallel to (00 I). H. =4. G. =2-46. Luster vitreous to 

 silky. Color light to dark brown. Opaque. In thin section 

 shows yellow color. Non-pleochroic. a = 1'62, y = 1*63. Opti- 

 cal axial plane parallel to (010). Comp. — Mn2Si^02g.7H20. Anal, 

 by Sahlbom, H,0 8'89, SiO, 35 '02, Al,03 0'75, FeO 5-80, MnO 

 37-20, Ca0 3-59, MgO 7*20, Na^O 0*12, K,0 1-13, other con- 

 stituents 0*19, Total 99 "89. Found on garnet crystals associated 

 with barite and calcite in the Norrbotten iron mine atLangbans- 

 hyttan, Sweden. ISTame derived from iKrpoTrrj, evasive, in reference 

 to the difficulty in determining its characters. 



Flokite. Karen Callisen, Medd. Dansk. Geol. For., v, Ko. 9, 

 1917. — Monoclinic. In thin slender prismatic crystals measuring 

 1-1^ cm. in length by ^ mm. in thickness. Observed forms : 

 (110), (100), (010). Faces vertically striated, (100) : (110) =: 

 41° 18'. Sections parallel to (010) show twinning on (100). 

 Cleavage perfect parallel to (100) and (010). Conchoidal fracture 

 across prism zone. H. =5. G. = 2 '102. Luster vitreous. Crys- 

 tal transparent and colorless or with faint gold-green tint. At 

 times dark colored from inclusions. Thin sections perpendicular 

 to prism zone show a division into segments with different optical 

 orientation. In the center of crystal the optical axial plane is 

 perpendicular to (010). b = y, c : a = about 5°. Axial angle 

 large. Acute bisectrix probably nearly parallel to c axis and 

 mineral is negative. In ISTa-light a — 1'4720, y= 1*4736. On 

 warming to 117°-118° sign of double refraction changes. Comp. 

 — A zeolite, IIg(Ca, NaJAl.SigO^g. 211^0. Anal, by Christensen ; 

 SiO, 67-69, Al,03 12-43, MgO 0-09, CaO 2-65, Na,0 4*36, H^O 

 13 '35, Total LOO-57. B. B. fuses easil}^ with intumescence. 

 Insol. in boiling HCl. Found on an old specimen in the Museum 

 at Copenhagen labeled from " Eskefjord ? Iceland." ISTamed after 

 the viking Floki Yilgerdarsen, who gave Iceland its name. 



Mar garo Semite. This mineral, recently described from Frank- 

 lin, N. J. by Ford and Bradley (this Journal, xlii, 159, 1916), has 

 been found by Gustav Flink at Langbanshyttan, Sweden (Geol. 

 For. Forh., xxxix, 458, 1917). The Swedish occurrence shows 

 slender prismatic crystals, often in radiating groups. Usually 

 the crystal faces are striated or curved. A few small and well 

 developed crystals were observed upon which measurements were 

 made. Triclinic. a:b:G =z 0*73998 : 1 : 1-2849 ; a = 74° 37', 

 ^=50° 28', y=78° 53'. Observed forms, a (100), b (010), m (110), 

 ?i(110), c(OOl), 6? (Oil), e(034)? Cleavage in three directions, 

 b (010), very perfect, c (001) and (504) (not observed on crystals) 

 good. Found associated with schefferite, apophyllite, calcite, 

 nasonite and thaumasite. 



