128 Genth and Penfield — Lansfordite, JVesquehonite, etc : 



unaltered lansfordite. For more ready comparison we have 

 given the calculated percentage composition of both nesque- 

 honite and lansfordite. 



From the above observations we conclude that the lansford- 

 ite is very unstable, losing its water and changing into nesque- 

 honite at a very moderate temperature. Under ordinary con- 

 ditio} is this change goes on so rapidly that only microscopic 

 crystals are developed and perfect pseudomorphs are formed. 

 In the mine, where we should expect the temperature condi- 

 tions to be uniform, the change undoubtedly went on slowly 

 and quite large crystals were formed. We should not expect 

 the summer temperature in the mine to be as high as out of 

 doors, and what agency had been at work in bringing about 

 the change other than rise of temperature we do not know. 

 It is probable that the lansfordite was discovered very soon 

 after its formation and we feel that we were very fortunate in 

 obtaining it before its conversion into nesquehonite. 



Crystallization of lansfordite. 



Lansfordite is at present only known in pseudomorph crys- 

 tals ; these are, however, so unlike anything which we have 

 ever seen before that they have been subjected to very careful 

 crystatlographic study. They are exceedingly interesting as 

 they show a curious combination of stalactitic and crystal 

 growth. The stalactites are mostly round and tapering like 

 ordinary stalactites, but on and near the ends they have per- 

 fectly flat crystal faces ; these have rounded contours where 

 they join the curved surface of the stalactites and frequently 

 two crystal faces, instead of coming together forming, a straight 

 edge, are separated by a curved stalactitic surface. On looking 

 over the material, at first all hopes of measuring the crystals on 

 a reflecting goniometer by direct reflection of lignt was given 

 up as the faces seemed too dull for that purpose. Two of the 

 crystals were therefore laboriously measured by placing a little 

 Canada balsam on the faces and pressing small bits of thin 

 cover glass upon them before placing them on the goniometer. 

 This method gave rather unsatisfactory results, especially for 

 the smaller faces and was soon abandoned, as it was found that 

 in cleaning up the crystals with alcohol and wiping them- with 

 cloth a slight polish was developed on the faces, causing them 

 to give a slight reflection of light, sufficient for an approxi- 

 mate measurement of the angles by using a strong illumination 

 and the low ocular (8 of Websky) on the Fuess reflecting goni- 

 ometer. It was also soon found that most of the crystal faces 

 were so smooth and perfect that without any polishing they 

 gave, with strong illumination and a low ocular, a fair reflec- 

 tion of light. Altogether there were sent to New Haven 



