Genth and Penfield — Lanrfordite^ \ iquehonite y etc. 125 





i. 



ir. 



in. 



IV. 



Average. 



Etatlo. 







30-18 





30-26 



30-1-2 



•681 r 





TO-56 





TO'53 









MgO 



29*4 l 



■ u 



29-18 



29-0 I 



._> ,).._)•_) 



■731 106 



HoO _. 











\o:v> 



2-240 3-26 



99-76 



The ratio of CO, : MgO : II..O is about 1:1: 3, agreeing with 

 the formula MgCO t .3H^O. The calculated percentage com- 

 position of a mineral with the above formula being: 



CO 31-38 



MgO _ 28-99 



H^O 39-13 



which also agrees closely with chemical analysis. 



A rtificial nesquehonite. 



A salt of the composition MgCO t .3H,0 is most readily 

 obtained by dissolving magnesium carbonate in water con- 

 taining carbon dioxide and allowing the solution to stand till it 

 deposits crystals. The preparation of this salt we find men- 

 tioned in Klaproth's Chemisches Worterbuch, edition of 1808, 

 where it is stated that it crystallizes in transparent six sided 

 prisms, terminated by a six-sided basal plane, but the water of 

 crystallization is not mentioned. In Berzelius' Chemie, edi- 

 tion of 1S35, the same method of preparation and description 

 of the salt are given with mention of the three molecules of 

 water of crystallization. In 1855, Marignac* published hts 

 results of the crystal lographic measurement of the crystals, 

 which he describes as brilliant but deeply striated orthorhombic 

 prisms. He observed <?, 001, O; b, 010, i-i\ m, 110, /and 

 d. 011, 14, the same forms which occur on the natural mineral. 

 His measurements are : 



Marignac. Nesquehonite, Penfield. 

 m^m 110 ^ 110 64° 65° 36' 



d* rfOll ~01l 47 49 6 



We prepared a quantity of the salt, which crystallized 

 in radiating tufts of prismatic crystals. Individual crystals 

 were scarcely over 0'2 n,m in diameter and about 2"0 mm long. 

 Most of them were terminated by a simple basal plane and 

 showed either a rhombic or hexagonal cross section according 

 as b, 010, was wanting or present. Sixteen of these little crys- 

 tals were measured on the reflecting goniometer in hopes of 

 finding one which would give sharp reflections of the signal, 

 but owing to the small size of the crystals and some physical 

 unevenness of the faces the angles admitted of only approxi- 

 mate measurement and showed considerable variation. The 

 prismatic angle varied from 61° 30' to 68° 45', most of the 



* Mem. de la Soc. de Phys. and D'llist. Nat. de Geneve, xiv, p. 252. 



