| Small Scale Production of Lime for Building |
|1. General Information|
The colour of most limestones is varying shades of grey and tan. The greyness is caused by the presence of carbonaceous impurities-and the tan by the presence of iron.
It has been found that all limestones are crystalline but with varying crystal sizes, unit formity, and crystal arrangement. This ret suits in stone with a corresponding variance in density and hardness (Boynton p. 21). For lime production purposes there are two factors related to limestones' crystallinity and crystal structure which are of specifc interest:
Density or porosity is determined as the percentage of pore space in the stone's total volume. It ranges from 0.3% - 12%. At the lower end are the dense types (marble), and at the upper the more porous (chalk). Generally, the finer the crystal size, the higher the porosity but there are anomalies which suggest that each case be considered separately. A high porosity makes for a relatively faster rate of calcination and a more reactive quicklime.
Limestone varies in hardness from between 2 and 4 on Moh's scale with dolomitic lime being slightly harder than the high calcium varieties. Limestone is in most cases soft enough to be scratched with a knife. Marbles and travertines have the highest compressive strength whilst chalk has the lowest.
Due to the variance in porosity, the bulk densities of various limestones range from 2000 kg/m3 for the more porous to 2800 kg/m3 for the most dense.
The specific gravities of limestones range from 2.65-2.75 for high calcium limestones and 2.75-2.9 for dolomitic limestones. Chalk has a specific gravity of between 1.4 and 2.