Need help w/ID

[rockman1944]

Given to me by a gentleman from Texas just yesterday on a rock outing. Supposedly his neighbor has several of these on his acreage on the ground. Appears to originally been a nut of some kind before it petrified. Appears to be of the limestone nature. I put it in a muratic/water bath momentarily and the liquid goes crazy with bubbles dissolving it. It is now 1/8 smaller than it was but everything is still holding its shape, especially the two small hooks at the top. The color in the pics are the actual colors. I do not know if a brown colored nut will be revealed once it gets smaller or if the entire specimen is of limestone. Any ideas on what it may be? I am at a loss.

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[eechler]

What you have is a internal cast of a Protocardia texana, (Texas heart clam, or deer heart). The cast is known as a steinkern.

Muratic acid is not the best way to clean the texas limestone fossil's. I found this out cleaning a bunch of heart urchins from Fort Worth. They all started out with nice stars - but the stars bubbled away.

[rockman1944]

Thank you kindly eechler. Your description of what is is, does make sense.

[feidzd]

really?haha,so funny.