BY W. F. PETTERD, C.M.Z.S. H 



21. Aplome fOrthosilicate of Calcium and Iron). 



A garnet occurring in various shades of brown, but 

 usually of a cinnamon colour. The crystals occur in con- 

 siderable plenty and somewhat large size, often reaching 

 above an inch in diameter. When freshly broken out of 

 the matrix they are often well-developed rhombic dode- 

 cahedra with an attractive polish. 



Locality : In the west bank of the Upper Emu River, 

 near the Hampshire Hills. 



22. Arfvedsonite ( Mttasilicate of Sodium^ Calcium, and 



Iron). 



A soda amphibole which is peculiar to nepheline syen- 

 ite and rocks of the alkaline class. The only recorded 

 occurrence is " a highly ferruginous variety of amphibole 

 or black hornblende, containing 1 per cent, of copper. The 

 copper which it contains exists in part or all as oxy 

 <;hloride coating the crystals " (G. Foord). 



Swan Island, Bass Strait (Gould, Pro. Roy. See, Tas., 

 1871). 



23. Aragonite (Carhonute of Calcium). 



This mineral is not by any means abundant in this 

 State. It is dimorphous with and differs from ordinary 

 oalcite : which difference may be summarised as follows : — 



Calcite— 



Crystals, rhombohedral. 

 Specific gravity, 2 "7. 

 Hardness, 3. 



Deposited from cold solutions or from solutions col- 

 taining alkaline silicates. 



Aragonite — 



Crystals, orthorhombic. 

 Specific gravity, 2 "9. 

 Hardness, 3*5 to 4. 



Deposited from warm solutions, or from solations 

 containing gypsum or strontianite. 



The hard Tertiary basalt at Derby has afforded a few 

 well-developed bunches of long slender crystals, showing 

 acute pyramids occasionally radiating from the matrix. 

 They occur in the vughs with zeolites and a little amor- 

 phous calcite. This mineral also occurs under similar 

 conditions in the basalt of Middlesex, Mt. Bischoff, Shef- 



