[grahamJ THAUMASITE " 197 



common to the zones [ilfQx] and [mQS], so that the symbols of these 

 two forms are definitely fixed by the zone law. 



The crystal on which the new forms were observed is colourless 

 and transparent, and rather more than one-eighth of an inch in length. 

 The other forms present are shown in the figure, which gives the 

 approximate relative dimensions of all the forms occurring on the 

 crystal. All the new forms appear on both halves of the twin. 



The specific gravity, as determined by immersion in methylene 

 iodide, is 2-605; this is the value found by Day for pure artificial 

 albite, and it would indicate that the crystal is relatively free from 

 lime. 



The albite is associated with very pale brown dolomite, in simple 

 rhombohedra. The specimen came from the Harvey vein of the 

 Ascot Mine, Range VIII, Lot 8 (West half), Ascot Township, Sher- 

 brooke County, Quebec. 



Thaumasite from the Corporation Quarry, Montreal 



Some time ago the writer collected, at the Corporation Quarry, 

 a specimen of crystalline limestone which was coated along a joint 

 plane with a thin deposit of a soft white mineral, and a preliminary 

 examination indicated that this was thaumasite. During a recent 

 visit to the quarry, several larger specimens of better material were 

 obtained, and it was possible to confirm the identification and make an 

 analysis of the mineral. 



The Corporation Quarry is situated immediately below the 

 northwestern shoulder of Mount Royal, and it affords excellent 

 exposures of the intrusive contact between the nepheline syenite, of 

 which this side of the mountain is largely composed, and the Trentçn 

 limestone. The latter has been altered to a crystalline limestone, 

 and both it and the nepheline syenite are traversed by a number of 

 dykes, while all these rocks are intersected by joint planes. 



The thaumasite occurs near one of these contacts, usually as a 

 thin coating on narrow joint planes, which may be continuous through 

 the syenite, limestone, and one or more dykes; but so far as observed, 

 the mineral is mainly coating joint planes within the limestone. 

 The thaumasite is white, with a dull silky lustre, and forms crusts 

 made up of fibres with a feathery or somewhat radial arrangement; 

 beneath this there may be a thin layer of more compact material, 

 also thaumasite, which rests directly on the limestone or other rock. 

 In one case a joint plane traversing the nepheline syenite had been 

 first coated with crystals of calcite and upon these the thaumasite 



