Answer: I think I know! What you describe is called Desert Rose Gypsum. They are clusters of gypsum crystals which have grown in sand and have inclusions of sand or earth in the crystals (hence the yellow/brown color). Gypsum is a hydrous calcium sulfate. It is translucent to opaque and is found in white or light tones of yellow, brown or red.
You can do a Google search or you can see photos of the different kinds at the following website:
Hope this information is helpful!
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