this second line of pictures is from spicules that are from the air - water interface - showing that the X-tal shapes are better developed although there is lots of biogenic/organic/polymeric material around.Growth seems by spiral disslocation mechanism.
the last 4 pictures show the calcite surface details as well as some strange structures about which at this time I have no clue what they are - anyone??
(1)(2)(3)(4)(5)(6)(7)(8)
 

this line of pictures is from a piece that was fully out of the water but via capillary action still 'wet' - it shows that the calcite's are rounded and fractal - as in the previous cases - but that there are much larger biogenic filaments )see scale in first two pictures - presumably cyanobacterial mats that grow in symbiosis with the smaller filaments.
Pictures 5+6 show a calcite X-tal and it's surface that seems to have grown possibly via a spiral disslocation mechanism
(1)(2)(3)(4)(5)(6)(7)(8)
 

these two pictures are from a rim piece and they shown bacterial mate - similar to the sample before - but also large structures that are presumably plant material
(1)(2)