Dear Conch-L readers, I am writing my disseration on shell bead production in prehistoric Ecuador. I am hoping that you can help me fill in the gaps in knowledge of shell structure. One of the main subjects of the research is beads made from Spondylus sp. In Ecuador the species involved are Spondylus princeps and Spondylus calcifer (and possibly Spondylus leucacanthus). Many of the beads that I have recovered from archaeological sites (most dating to less than 2000 years ago) are what I call ROP beads. ROP beads are red, orange, purple or a combination of the three colors since often a single bead will have more than one color. These colors occur mainly in the outer crystalline layer of the shell as well as along the margin. From my inexperienced view, the ROP beads have a texture that white beads (which could have either been made from the interior of Spondylus shells of from other species) do not have. I know that shells can be made from aragonite and calcite (and sometimes vaterite) and that there are three basic types of structures, including prismatic, foliate or laminar and crossed lamelar. However, on an article dedicated to Spondylus, Skoglund and Mulliner indicate that Spondylus lacks "simple, prsimatic calcite; crossed-lamellar aragonite prominent". The reference is to Waller 1978, which has a single paragraph description that includes this statement. This makes it sound like the strucure of the Spondylus shell is relatively uniform. If this is true, then there should be no difference in the crystalline structure of the inner and outer crystalline layers. This would seem to indicate that my observation that the colored part of the Spondylus shell has a different texture and, therefore a different crystalline structure, is incorrect. I am attempting to show why these ROP beads are much more apt to break during production and, based upon my own qualitative observations, I believe this has to do with the 'texture' of the crystallin structure of the bead. Can anyone enlighten me as to why the texture seems so different when (based upon on citation) the crystalline structure is supposed to be the same. Thanks for any input. Ben Carter ---------------------------------------------------------------------- [log in to unmask] - a forum for informal discussions on molluscs To leave this list, click on the following web link: http://listserv.uga.edu/cgi-bin/wa?SUBED1=conch-l&A=1 Type your email address and name in the appropriate box and click leave the list. ----------------------------------------------------------------------