:::grinning while growling:: I just HATE not knowing the 'absolute answer' to this question (and I've been pondering it for quite awhile).
Kervran proved that chickens could convert the silicate of potassium in mica to calcium (book: Biological Transmutations). This was done by giving the chickens ZERO calcium in their feed until they produced 'softshell' eggs, and then giving them mica (which they went nuts over)...and afterwards their eggs again became calcareous. (In his youth he'd witnessed their own free-range chickens pecking out the mica flakes from the granite and always laying strong-shelled eggs, even though there was no limestone in the area...even though the chickens were never given any type of 'supplement'. So when he became a researching scientist, he did the research).
This shows that a chicken can 'biologically transmute' one mineral into another (Kervran also proved that humans convert the silica in horsetail grass into calcium)...which should mean that the calcium in egg shells is bio-available to us.
I've never searched my "Complete Works" of Dr. Christopher CD for this, because I know he's "anti meat/dairy" and he has an 'Herbal Calcium' formula that he consistently recommends for calcium needs...but maybe there'll be something there that will guide us further...be right back...
...Well, butter my buns n' call me a biscuit...BINGO!!!!
Another type of natural calcium is found in the use of eggshells. A chicken consumes grit and sandy materials, and these materials go into and through the gizzard into the blood stream. Then these calcium-type materials are taken from the blood stream to form the egg shell. After breaking the eggshell open, be careful to pull out the small membrane that lines the shell. This membrane is high in cholesterol and it is wise to eliminate it. Dry the shells at room temperature or under 130 °F. When thoroughly dry, powder the shells in a blender, nut mill or with a rolling pin. When the powder from one dozen eggshells is ready and finely powdered, cover with one pint of apple cider vinegar or one pint of lemon juice (lemon juice will sour and spoil quicker than the apple cider vinegar). Mix the eggshell powder and liquid in a large container, because the chemical reaction will cause the solution to foam.
For the adult, use two or more tablespoons (or add to distilled water, tea or juice if desired) and for children in proportion. Some people like to add a tablespoon of honey for each tablespoon of the vinegar-calcium mix, as this is a great help in adjusting the hydrochloric acid balance in the body as well as feeding calcium to the system (read Cyril Scott's book on Folk Remedies).
>>>Is it greatly worth while to use this calcium vinegar?<<< Apparently the answer is a resounding YES!!!
Fantastic!!! I'm SO psyched - sure this means we'll likely be selling less of the Herbal Calcium, but man-oh-man, this is AWESOME for folks that don't have the money to buy it...and as soon as I find the time, I can "upgrade" the ACV Bomb to include "calcium vinegar". Do I love this forum? YES!!!