The listing, USA #1002 1951 American Chemical Society, mint has ended.
USA stamp commemorating the ACS - American Chemical Society
Year: 1951
Catalog # 1002
Condition: full gum, mint never hinged, post office fresh
I have several of these stamps, all identical, the scan is representative of what you will receive.
My general terms for stamp-related Listia lots can be found here (please read, it answers a lot of basic questions):
http://listiarules.webs.com/