Thanks for the all the interest in the blocks I showed here. I've had several enquiries about the block, so here are the details:
The block is called Midsummer Night, a Nancy Cabot block from Barbara Brackman's Encyclopedia of Pieced Quilt Patterns. If you have the BlockBase software library of blocks, it is block 3070.
Gorgeous, isn't it? I've been wanting to make a quilt with this block for years. I plan to write a pattern for it after I have finished my quilt, but I am hand-piecing so will be some time yet.