Southern India forms predominantly a granitic terrain with numerous varieties of granite and granitic gneisses, charnockite, alkaline rocks etc. Within this vast granitic complex, deposits of quartzite, sandstones, marble are found in significant quantities. The resources of granites (in a general sense), charnockites etc. suitable for mining dimensional stones have been described by many. Of late, the importance of the physical properties of these dimensional stones are being felt by different user agencies. Although the data on resources of dimensional stone is abundant, information on their physical properties is scant. In this paper, a review of the data available to the authors on physical properties of different rock types occurring in Karnataka, Andhra Pradesh and Tamil Nadu have been attempted. Thrust areas for further work have also been indicated. Whether a 'stone' has been quarried as dimensional stone or for other purposes (building stone), it is essentially a rock type and the physical properties have the same meaning and significance. The important physical properties of rocks are: (1) Specific gravity, (2) Porosity, (3) Water absorption, (4) compressive strength, (5) Transverse Strength, (6) Shear Strength, (7) Durability, (8) Weathering, (9) Reflectance and (10) Parameter Vs Climates.

     

The principal rock types presently being quarried in the three southern states are migmatitic gneisses, porphyritic and homophanous granites, chornockite, leptynite, alkaline granites, gabbro, dolerite and anorthosite.

 

For Karnataka, data for about 334 locations have been reported by Karnataka Engineering Research Station (KERS) while for Andhra Pradesh, data has been reported by Andhra Pradesh Engineering Research laboratory, Public Works Dept., Tamil Nadu has reported data for rocks of Tamil Nadu (as in 1979). The table below summarises the work of these organisations.

 

Besides the Department of Mines and Geology, Karnataka, has furnished compressive strength values for 253 locations as follows:

   

As seen from the source publications, it is observed that two or more samples from an area have been studied. It is not clear whether the samples represent petrographic varieties from a single quarry or from different quarries around a given locality.

   

Although the reports contain data on many physical properties, only some of them have been discussed in this paper. The rock type-wise ranges of values are furnished below. In Table II details of samples under different rock category are furnished.

   

The number of samples of quartzite, limestone, dolerite etc., is negligible and hence not presented. Interested readers may refer to Bureau of Indian Standards publications for details.

 

The ranges in values of compressive strength reported by Dept. of Mines and Geology, Karnataka are as follows:

  

The data presented above shows that the gneisses and granites form the main rock type studied. This is perhaps due to their utilization in routine building construction and related civil works. Many other important rock types now quarried for dimensional stones have received lesser attention. Even the gneisses and granites which form a major part of the hard rock, resources of the three southern states should be regarded as less studied compared to their wide petrographic variants and areal extent of this group. It is also observed that high foreign exchange earners- dolerite and gabbro commercially known as black granites have not received much attention. It is apparent that there is a need and scope for further contribution of physical property measurements on south Indian 'granites' or dimensional stones. A large number of data are required for defining meaningful range and average value for the physical properties. Keeping this in view, a few suggestions are made:

 

 

A data-base for different petrographic variants of gneisses and granites is to be prepared. This initially can be made in respect of identified dimensional stone resources in the granite gneisses- regions.

Physical property determinations on these petrographic types.

Physical properties determination on the charnockites and leptinites and enderbites in the eastern ghat belt of Tamil Nadu, Kerala and Andhra Pradesh and also on the massive charnockits of Karnataka.

Alkaline granites, syenites and anorthosites have gained importance as dimensional stones in view of their colours and textures. These need to be studied for their physical properties.

Dolerite and equivalent mafic rocks occur abundantly as dykes and sills and contain many petrographic varieties. The international as also domestic market has opened up for types hitherto not used. There is scope for detailed work on the mafic rocks of South India.

The quartzite and sandstones of the Cuddapah in the proterozoic and younger sedimentary belts in South India form potential sources of dimensional and decorative stones. So are the meta quartzite in the Precambrians. As such, available data is meager and there is scope for study.

An important aspect which needs to be carried out are reflectance (polish ability)and charge of physical properties of different dimensional stones with climate changes. It is pointed out that dimensional stones in both unprocessed and as polished slabs are largely exported to countries with radically different climate conditions.

At present, the facilities for physical property measurements for rocks are available in Govt. institutions and research laboratories in public sector. The AIGSA should co-ordinate and build up collaborative projects, in view of the large volume of work lying ahead. Alternatively, the AIGSA can establish a 'Stone Research Laboratory" at Bangalore for the benefit of the industry if the Government institutions are facing constraints like manpower budget etc.

The AIGSA should compile specifications of the importers and publish periodically for the benefit of the Members.

 

References:

 

Schedule for properties and availability of Stones for construction purposes. Pt.4. Karnataka Sec 1-3 (1996), IS 7779 Bur. Ind. Standards.

Schedule for properties and availability of stones for construction purposes, Part 5 Andhra Pradesh Sec.1-3. IS 7779 (1997). Bur. Ind. Standard, New Delhi.

Schedule for properties and availability of stones for construction purposes, Part III Tamil Nadu State Sec.2, IS 7779 (1980), Indian Standards Institute, New Delhi.

Raghuveer, Lalgondar, B.A., Jayaram S (1997), physical properties of rocks with Special Reference to Ornamental Stones of Karnataka's Geological Studies 272, Dept. of Mines & Geology, Bangalore.