208 the minerals of new south wales. 



Halloysite. 



Chem. comp. : Hydrous silicate of alumina. 



This is an amorphous earthy mineral, resembling steatite, derived 

 from the decomposition of igneous rocks. Adheres to the tongue, 

 can be scratched and polished by the nail ; of various colours — 

 black, brown, grey, green, and red j the black often contains small 

 brilliant white veins. When placed in water the mineral usually 

 falls to pieces, and the edges become translucent. 



Specimens of black halloysite are from time to time brought 

 from all parts of the Colony as samples of graphite. 



Occurs in railway cutting through decomposed basalt containing 

 chabasite at Reedy and Stony Creeks, Sutton Forest ; at Two- 

 mile Flat of a pretty green colour ; Carcoar and Lachlan River. 



Zeolites. 



This group of minerals is distinguished by the property which 

 most of them possess of fusing with intumescence before the blow- 

 pipe, i.e., they boil up, the name being derived from t,r)io, to boil, 

 and \lOos, a stone. The are usually found filling the amygdaloidal 

 cavities and crevices in igneous rocks, and never as crystals 

 disseminated through the mass of the rock like pyrites, garnet, or 

 mica. In chemical composition they consist essentially of com- 

 pound silicates of alumina, the alkaline earths and alkalis ; and 

 when treated with acids gelatinous silica is separated. 



Stilbite. 



Chem. comp. : Hydrous silicate of alumina and lime. Rhombic 

 system. Reported to occur in metamorphic silurian shales at 

 Adelong. 



Laumonite. 



Chem. comp. : Hydrous silicate of alumina and lime. Oblique 

 system. This mineral occurs in the form of white crumbly pris- 

 matic crystals in association with black and white particoloured 

 calcite crystals in the cavities of an amygdaloidal rock on the 

 road between Geringong and Kiama. 



There is a pink mineral in slate on the Mudgee Road, found by 

 Mr. Wilkinson, which is probably a laumonite. (For further 

 particulars see Report upon New South Wales, part I., p 20.) On 

 analysis this mineral yielded the following results : — 



Silica ... 53-266 



Alumina, and trace of iron oxide ... 22*833 



Lime 11-000 



Water of combination ... .. 12-646 



Specific gravity, between 2-3 100,224 



