Biological Transmutations and Their Applications in Chemistry, Physics, Biology, Ecology, Medicine, Nutrition, Agriculture, Geology by Professor Louis C Kervran is an investigation into the possible natural changing of elements into different forms by life forms such as animals and plants through non nuclear and low energy transmutation.
Ninety-seven percent of the egg shell consists of calcium carbonate. The shell weighs approximately 6.0 g, so almost 6.0 g of calcium carbonate must be synthesized and deposited on the shell each time the hen produces an egg. For many hens, this is almost daily for long sequences.
Calcium carbonate is 40% calcium, thus about 2.5 g of elemental calcium must be found and transported to the shell gland in the 18-20 hours it takes to form the egg shell. The calcium content of blood at any given time is no more than 30 mg. Thus the shell contains over 80 times more calcium than the content of the blood.
Calcium sources for laying hens by Dr Peter Hunton (PDF)
The original French version of the Biological Transmutations book by Corentin Louis Kervran was published a long time ago in 1962. Kervran wrote a number of follow up books. Michel Abehsera combined C L Kervran’s books into an English translation that was published in 1972.
You can read an article and sort of book review on the Biological Transmutations book and calcium.