April '/t/i,igoS.] Proceedings. xxi 



Mr. R. L. Taylor, F.C.S., communicated a paper by 

 Mr. Robert Pettigrew, entitled "On the Occurrence 

 of Quartz Crystals in Limestone, Columnar Coal, 

 Marble, &c." 



Photographs, microscopic and lantern slides were exhibited, 

 showing beautiful microscopic crystals of quartz obtained from 

 mountain limestone, columnar coal from Airdrie, in Lanark- 

 shire, and ordinary statuary marble. Attention has been pre- 

 viously drawn to the occurrence of these crystals in limestone 

 and marble,* but most of the members of the Society present 

 had not had an opportunity of seeing them. 



The crystals from limestone and marble are obtained by 

 dissolving some quantity of the material in hydrochloric acid 

 and treating the insoluble portion with strong sulphuric acid and 

 a little potassium chlorate to destroy the organic matter, and 

 then mounting in the usual way. The columnar coal, from 

 which some of the specimens were obtained, resembles in some 

 respects a well-burned coke. It comes from Airdrie, in Lanark- 

 shire, and has been metamorphosed through an intrusive mass of 

 basalt forcing its way along the seam of coal, with the result 

 that the coal has been "coked" to a columnar mass. From this 

 coal the crystals are obtained by grinding it coarsely and washing 

 away the coal. 



The crystals from both the limestone and the coal are 

 mostly well formed double-ended quartz crystals, in many cases, 

 especially in the smaller crystals, the facets being perfect, as if 

 polished. They vary in size from about yoVsj'^h ^° r^o^h of 

 an inch in length. When mounted in Canada Balsam (which 

 has almost the same refractive index as quartz), a hazy outline 

 only of the crystal is visible, but nearly every crystal shows a 

 dark nucleus on which the crystal has been built. It is Mr. 

 Pettigrew's opinion that this nucleus has been at one time Iron 

 Pyrites, although it is now mostly oxidised to the brown oxide 

 of iron. 



The crystals in marble, owing to the pressure and meta- 

 * J. Barnes, Trans. Manchester GeoL Soc, vol. 27, part 15. 



