97 



in the Museum of Copenhagen we can see that the cavities 

 which contain the gyroiite must have been of a considerable 

 size, at least 1 — 2 dm in diameter. 



The minerals which accompany the gyroiite are mesolite 

 and apophyllite, and the succession of these is very distinctly 

 the following: mesolite, gyroiite, apophyllite. The mesolite is 

 developed in spherical radiated aggregations of a diameter of 

 c. 1 cm which cover the walls of the cavities and from which 

 free needles protrude into the gyroiite but only attain the length 

 of about 1 mm. The gyroiite forms a stratum on the inner 

 side of the mesolite and the thickness of that stratum varies 

 from 1 to at least 5 cm; from that some folia protrude into 

 the apophyllite, which mineral is only found in one specimen 

 and which consists of one very large individual (about 5 cm 

 in diameter) without distinct crystalline faces; it seems that 

 its form has been partly influenced through contact with other 

 individuals of the same mineral which no longer exist. 



The gyroiite is, as is otherwise the case, crystallized in 

 radiated, foliated groups; the common size of the folia varies 

 from 0"5 to 2 cm, the arrangement of the folia is however not 

 so regular as commonly, for distinct spherical aggregates are 

 not to be found, and the folia are often seen to intersect each 

 other and in some places to form quite a complicated network. 



Here and there freely developed folia are seen to protrude 

 into small cavities and these have given me the material for 

 crystallographical examination. 



Crystalline form. The crystals have the habit of very 

 thin hexagonal tables, the edge of which is mostly, by altera- 

 tion as 1 think, quite uneven and without distinct faces; in 

 some cavities it is possible to find better developed crystals 

 with rather plane and shining marginal faces, which have al- 

 lowed the following measurements to be made. 



What is so far known of the crystalline form of gyroiite 

 is very little. Giesecke describes the form as hexagonal tables; 



