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mohd scale of hardness

Moh’s scale of hardness is as follows :

'1.Talc

2.Gypsum    Scratched by finger  .

3.calcite

4.Fluorspar  Scratched by a knife"

5.Apatite '

6.Orthoclasc  Sczirccly scratched by a knife.
7.Quartz ‘

' 8.topaz. . . .

9.Corundum Not scratched by a knife.

10. Diamond '

It may be observed that :

A finger nail will scratch upto about 2.5..
A pen knife will scratch upto 6.5

 When testing the hardness of mineral window glass can be used as a substitute for apatite. ‘ ,

Protodyakonov strength number : Hardness of rock is expressed by Protodyakonov strength number in Russia. The number indicates the relative ease with which a rock can be broken, e.g. strong lignitcs and weak clay shalcs have Protodyakonov strength number as 15 to 2; strong colas and am hracitcs have strength number as 2; exceedingly strong quartzites and gabbro diorites have the number as 20-25, the highest number. Other rocks have the numbers inbetween. 

Electrical and magnetic properties of minerals and the properties dependent on light are also made use of in distinguishing minerals which react in a distinctive manner to the tests.

Common Minerals

There are about. 107 elements that have been isolated and recognised in the labdratory. Of this number, however, there are only 8 that enter into the composition of the earth’s outer portions in abundance. In fact these 8 elements make up some 98% of the earth’s observable crust. These are (in order of abundance) :

 

The combinations of some of these eight common elements among themselves have produced the most common rock-forming minerals that constitute the bulk of the rocks These 


most common rock-forming minerals are feldspars, quartz, mica, amphiboles, pyroxenes and olivine. 


The other 96 elements are relatively scarce, in that they represent only 1.5% by weight of the earth’s crust e.g. Cu = 0.0045%, Pb = 0.00015%, Au 0.0000007%. There are about 2000 catalogued mineral specimens but the real economic targets of 


miming activity are 100 minerals including the native minerals, the hydro carbon minerals and a few types of economic rocks used as house construction materials. 


Of the above rock-forming minerals some can be considered as essential minerals while some others are accessory minerals and secondary minerals. 


(a) Essential Minerals: '

These make up the bulk of the rocks and are always silicates with the exception of quartz. and the cabonates. 


(b) Accessory Minerals: 


“these are present only In small quantities in a rock (c) 

Secondary Minerals 


. These are derived from the break-down of the others. 

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