154 building stones of queensland. 



General Remarks. 



The difference in character of stones obtainable from 

 the same quarry is not alwaj^ apioreciated. Igneous rocks 

 such as granites, trachytes, etc., are rather homogeneous 

 and there is little variation in the character of the stone 

 as a rule, provided it is fresh and unweathered. Sedimentary 

 rocks such as sandstones and limestones show great variation 

 and adjacent beds in the same quarry frequently vary to a 

 considerable extent. This is easily understood when one 

 realises the mode of origin of these rocks ; also the same bed 

 might easily change in character for better or for worse 

 as it is worked. The inspection of sedimentar}- stones 

 should, therefore, be very strict and each stone before 

 being used should be passed by a duly-qualified person as 

 being up to standard ; with igneous stones after careful 

 selection of the quarry the inspection need not be quite so 

 strict. 



A perusal of the Table of Crushing Strengths, etc., 

 shows how varial)le the resiilts may be for stone from the 

 same quarry. 



It is generally agreed that in correlating results of 

 Crushing Tests, little heed can be paid to the results obtained 

 on different machines by different ojoerators over a lengthy 

 period. The maimer in which the specimen is shaped and 

 mounted, the size of the cube and the condition of the 

 jaws, whether greased or lined with paper, cardboard, zinc, 

 etc., affect the I'esults obtained. 



The selection of the specimens to be tested is of course 

 an all-important matter, as a great variation exists in the 

 results obtained from the same stone when crushed wet 

 and dry. If a stone is taken from a quarrj^, dressed straight 

 away and crushed with the sap water still in it, lower re- 

 sults will be obtained than bj' the selection of a jDiece of 

 stone from the same bed, but which has been allowed to 

 dry thoroughly before dressing and crushing. 



The cracking pressure, the crushing pressure, the nature 

 of the report on crushing, the shapes and number of the 

 fragments, the sharpness of the edges an-d the amount of 

 powder, should all be noted. The sharper the report, the 

 keener the edges of the fragments and the smaller the 

 amount of powder, the better the stone. In any case the 



