We have some information on this website >>
http://shale.apache.org/ (You may have seen this website already)
Mainly Shale used with Another technology. So may be thats why there is not direct book. I am using Complete Reference
JSF book (Appendix D - for Shale Frame Work). It helped me a lot to understand what is shale. I hope it help you also.
Thanks
Sajan Patel