I am not sure what Ikaite is... but seems like scientists are trying to find out, too.
anhydrous calcium carbonates... even with the name Calcium in the name does not mean they are bio available to use by animals...... they may remain in crystal form and get pooped out...
ie.. there is tons of Iron in spinish, but it is not bio-available to be obsorbed by human...
http://www.cins.ca/aca/ikaite.html
http://en.wikipedia.org/wiki/Ikaite
I am trying to find out that answer myself, too. Very interesting... I haven't been talking to couple of my " supposedly very smart friends.." but so far the answer is still no calcium in shell...