Lithographic limestone
Lithographic limestone is hard limestone that is sufficiently fine-grained, homogeneous and defect free to be used for lithography. Geologists use the term lithographic texture to refer to a grain size under 1/250 mm. The term sublithographic is sometimes used for homogeneous fine-grained limestone with a somewhat coarser texture.
The generally accepted theory for the origin of lithographic and sublithographic limestones is that they were formed in shallow stagnant hypersaline and anoxic lagoons. The combination of mild hypersalinity and low oxygen content is believed to have inhibited the formation of microbial mats and prevented the invasion of bottom dwelling organisms. Microbial mats and bottom dwelling organisms would have left fossils, and bottom dwelling organisms would have churned the accumulating sediment, producing a less homogeneous rock. Stagnancy was required to avoid churning or sculpting of the sediment by currents or wave action.
The original source for lithographic limestone was the Solnhofen Limestone named after the quarries of Solnhofen where it was first found. This is a late Jurassic deposit, part of a deposit of plattenkalk (a very fine-grained limestone that splits into thin plates, usually Micrite) that extends through the Swabian Alb and Franconian Alb in Southern Germany. Only a small fraction of plattenkalk is suitable for lithography.
For many years, the Solnhofen deposits were the only source of lithographic limestone. French lithographic limestone from quarries near Montdardier, about 6 km south of le Vigan, Gard was exhibited at the Great Exhibition of 1851, where it earned an honorable mention. This stone is from the upper Lias Group, from the early Jurassic. The largest lithographic printing stone ever quarried came from Le Vigan, 230x150cm (90x59 in).Théophile Steinlen used a comparable stone for some of his posters. Several quarries are visible today on the chalky plateau above Montdardier, between 2 km north (43°56′54.46″N 3°35′3.44″E / 43.9484611°N 3.5842889°E), and 2 km west (43°55′52.61″N 3°33′38.78″E / 43.9312806°N 3.5607722°E) of the town.
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