MINERALOGY. G73 



rhombic system, and are sometimes tabular in habit through the ex- 

 tension of the brachypinacoid, but more frequently the basal plane pre- 

 dominates and the outline is hexagonal. The prismatic angle is 121° 

 20* , and twins with axe-entrant angle of about (50° have been observed. 

 The plane of the optic axes is parallel to the brachypinacoid, and the 

 acute negative bisectrix is normal to the macropinacoid. The crystals 

 are generally perfectly transparent, and either colorless or with a slight 

 tinge of 3*ellow. The luster is biilliant and vitreous. The hardness • . 

 nearly that of feldspar, and the specific gravity is 2.59. The chemical 

 composition of the mineral has been established by M. Damour. He 

 shows it to be a hydrous silicate of beryllium (glucinum), conforming 

 to the formula 2 Be 3 Si 4 + H 2 O; the water goes off only when the 

 mineral is subjected to a red heat. In composition, then, it is near the 

 rare mineral pheuacite, from which it differs in that it contains water 

 as well as in its physical aspects. Bertrandite has been found at the 

 quarries at Petit-Port and at Barbiu, in the neighborhood of Nantes. 

 It occurs implanted upon quartz and feldspar in cavities in pegmatite. 

 (Bull. Soc. Min., vi, 248, 252.) 



Dumreicherite. — In a memoir on the volcanic rocks and minerals of 

 the Cape Verde Islands, Doelter describes a new mineral of the alum 

 group to which he gives the name Dumreicherite, in honor of Baron von 

 Dumreicher, of Lisbon. It is a mineral of secondary origin, occurring 

 in crusts lining crevices in the lava. Under the microscope these 

 crusts are seen to be made up of an aggregate of fibrous crystals, whose 

 optical characters correspond with the mouoclinic system. Crystals 

 were obtained from a solution of the mineral, but they did not afford 

 the means of definitely fixing the form. The mineral has an astringent 

 taste, dissolves readily in water, aud melts in its water of crystalliza- 

 tion. Au analysis by F. Kertscher showed that in composition it con- 

 sists of four molecules of magnesium sulphate, one of aluminum sul- 

 phate, and thirty-six of water. 



Eichwaldite. — See below under Jeremejeffite. 



Empholite. — A new mineral from the remarkable locality of Horrsjd- 

 berg in Wermland, Sweden. It is described by Igelstrom, and named 

 from the Greek word signifying to hide, in allusion to the difficulty of 

 recognizing it in consequence of its minuteness and of its being cou- 

 founded with the inclosing gaugue. It occurs in very minute, white, 

 transparent prismatic crystals, with brilliant luster. According to au 

 examination by Mr. Bertrand, the crystals belong to the orthorhombio 

 system, with a prismatic angle of 128° to 130°; the cleavage is perfect, 

 parallel to the brachypinacoid, and yields brilliaut surfaces. The plane 

 of the optic axes corresponds to the direction of cleavage, and the acute 

 positive bisectrix is parallel to the brachydiagoual axis. The hardness 

 of the mineral is about six. Before the blow-pipe it is infusible, and 

 with cobalt solution it gives a deep blue. According to several analy- 

 ses it is essentially a hydrous silicate of aluminum, containing also a 

 H. Mis. GO- — 4o 



