품명 : 암모나이트(오팔)
학명 : Discoscaphite conradi
지층 : Fox Hills Formation
산지 : North Central,South Dakota,U.S.A
시대 : 중생대 백악기(Upper Cretaceous :  73 million years ago)
크기 : 14*12*5.5cm
내용 : 오팔로 치환된 대표적인 암모나이트 화석으로 미국 산이다. 모암에는 다양한 종류의 조개화석(완족류+이매패)들이 있으며 전형적인 퇴적의 구조를 지니고 있는 화걷으로 전문가급의 품질을 지니고 있다.
With immense natural aesthetics, this is a large portion of an original ammonite-bearing shale boulder displaying two complete (as well as multiple other partials) of beautiful natural white Upper Cretaceous ammonites. Most impressive is the presence of their original preserved shells that are thick and white with multi-colored, pearly iridescence seen in full light.  This effect did not photograph but is very obvious in person and must be seen as such to be appreciated.  This specimen is much, much nicer in person!  The original outer rind of the boulder is also still present.  This is a fantastic display piece with lots of educational value as well, since the matrix is large and has not been ground away and removed.  This shows what the original rock looked like where these rare ammonites were found.  Ammonites like these are not commercially mined so their scarcity is not only due to true rarity but also to the lack of any large scale efforts compared to mass-marketed and produced ammonites from Russia, Madagascar and Morocco.  Excellent horned anatomy is preserved as well as very delicate chamber detail.