Observations on embryonic chick-bone crystals by high resolution transmission electron microscopy.

High resolution transmission electron microscopy of bone mineral at a vary early stage in its deposition in embryonic chick frontal bone demonstrates crystals of 2-2.5 nm thickness and a profile up to 40 nm long. They appear in groups which may show as few as one or two crystals. Associated with the crystals is a less dense amorphous material. Using specimen tilting, the change in crystal appearance indicates that crystals are tablet-shaped (rectangular) rather than rod-shaped. The amorphous material may be tablet-shaped crystals in orientations which are not dense enough to register as crystals in the image. Truly amorphous mineral does not show by bright-field electron microscopy, but preliminary results indicate that the dark-field technique may prove to be useful in imaging amorphous mineral provided that sections can be cut thinly enough and that precautions are taken during specimen preparation to avoid mineral loss. Crystals have been located in various parts of the osteoid zone and were not associated specifically with any one component. Rapid processing using anhydrous techniques must be used to avoid the possibility of artefactually altering the in vivo conditions of the mineral at the time of excision of the specimen.