CRYSTALLINE COMPONENTS 65 



record their low birefringence and approximate refractive index. It is also clear that he 

 recognized and was puzzled by the difference in optical properties of the "envelope" 

 crystals and of the dumbbell-shaped spherulitic aggregates of whewellite sometimes 

 found in urine. Apparently he did not suspect the existence of two hydrates of calcium 

 oxalate. The largest envelope crystals detected in human urine by Golding Bird (1843) 

 measured 0-056 mm. across, but he found still larger light amber crystals, 0-17 mm. 

 across in horse urine (1845). These he preserved dry since they were "invisible in 

 Canada balsam". 



Although the deep-sea crystals are about ten times larger than those observed in plant 

 cells and ten times smaller than those from renal calculi, they are only a little larger than 

 urine crystals. The possibility that the deep-sea crystals have been deposited from the 

 urine of some marine organism is unlikely for three reasons, (i) Crystals deposited from 

 urine might well be expected in all oceanic bottom deposits, whereas Mr Earland's 

 extensive study of ocean bottom deposits from all over the world so far shows that the 

 "envelope" crystals are not only a minor constituent but are restricted to very deep 

 water in the Weddell Sea. (ii) Louis Heitzmann (1934) has observed that urine and renal 

 crystals of calcium oxalate turn black at first on slow ignition owing to included organic 

 tissue. The deep-sea crystals, however, change to calcium carbonate and at a higher 

 temperature to lime without change of colour, (iii) The deep-sea crystals possess sharp 

 edges and faces free from scratches so that there seems little doubt that they were 

 formed in situ. It is obviously important to continue the search for calcium oxalate 

 crystals in other ocean bottom deposits. The more urgent problem of the constitution 

 of the blue and red sea-bottom muds may have led mineralogists to overlook this rare 

 constituent. It is essential to make a careful study of oceanic deposits before removing 

 the calcium carbonate by digestion with dilute hydrochloric acid, since this treatment 

 would also remove calcium oxalate. 



Although the monoclinic hydrate, CaC.,04 . HgO, the more commonly observed salt 

 in plants (raphides) (Vesque, 1874) occurs as the mineral whewellite in coal measures 

 from various localities, the tetragonal salt has not hitherto been observed as a mineral. 

 H. Braconnat (1825) has indeed recorded a growth of lichen on limestone containing 

 nearly half by weight of calcium oxalate and J. Liebig (1853) named a similar in- 

 crustation, thierschite. Neither author, however, gives figures for the water content and 

 I have not been able to secure a specimen of the original material for identification. 

 A section of a lichen spore reveals irregularly shaped cr>'Stals which, however, prove to 

 be whewellite not the tetragonal salt. Thierschite should then be regarded as an un- 

 certain species since the name was given to the material on the basis of an incomplete 

 chemical analysis. It would also be unwise to give a mineral name to the tetragonal 

 crystals of hydrated calcium oxalate from the Weddell Sea deposits until the dihydrate 

 formula is placed beyond question. 



The origin of calcium oxalate in the ocean bottom mud of the central Weddell Sea 

 is entirely conjectural. The writer finds it impossible to suggest how any sedimentary 

 constituent of the earth's crust can be restricted to one small region, more particularly 



