While the carbon of this blog is organic combustible carbon, this post strays from that material to “burnt lime”, a manufactured calcium oxide made from burning limestone, which is mostly the carbonate mineral calcite with the formula CaCO3, which does contain carbon.
Why “burnt lime”? Because I came across this very white stone (photo below) in my Lafayette College community garden plot which sits on former and adjacent to current farm land in Forks Township, Northampton County, Pennsylvania. Geologically, the community farm is on the Epler Formation of the Lower Ordovician Beekmantown Group. The older Cambrian and younger Middle Ordovician formations enclosing the Epler are also limestone or dolomite (CaMg(CO3)2), originally deposited in a large carbonate shallow sea, similar to the Bahamas platform, on the passive margin of the paleo-North-American continent, Laurentia. Geographically, this is the “Great Valley”; economically, the Great Valley is the “cement belt” while the outcropping younger Upper Ordovician deep-ocean Martinsburg shale to the north is the “slate belt” (see also post from January 2016 on “Geology and Gerrymandering”).
Besides cement, local limestone was quarried for lime (CaO) as a soil amendment. In 1941, Benjamin L. Miller (Lehigh University Professor of Geology) wrote:
“Limestones for lime- More limestone quarries in Lehigh County [note- Lehigh County is just west of Northampton County] have been opened to get stone for burning than for any other purpose. Most of them are small and are now filled with rubbish and the kilns nearby are in ruins. Almost every clump of trees in the fields conceals one of these abandoned quarries. Of course, many of the quarries were opened along the stream bluffs. Years ago it was the common practice for the farmers to quarry and burn the stone during seasons when there was little work to be done in the fields. The kilns were constructed of field stones, many of glacial origin, and wood was used for fuel. The burning was not very efficient and the limed fields now contain pieces of chalky-white, partially-burned stone that may have lain there for many decades. Students have been puzzled by these limestone fragments, so unlike the other limestones in appearance. The farmers felt that it was profitable to add lime to the soil every three to five years and by a definite program one-third to one-fifth of the farm would be limed each year.
“Although the great bulk of the lime produced was used for improving the soils, at all periods the lime needed to supply the local demand for mortar also came from these same kilns.“
[Pennsylvania Geological Survey, Fourth Series, Bulletin C39, Lehigh County Pennsylvania Geology and Geography (1941) (p. 369)]
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| Burnt lime found in community garden plot on old farmland. |
