Krishna the Supreme mystic has placed so many things all through the world to be used in His service, and for the benefit for the people in general. So many mysical things, wonderous things, inexplainable things - similarly the Moqui stones have been used by Shamanic priests and healers for centuries. However, as you read here in the links below they are intrinsically different from Shalagrams and while themselves it appears have some power/potency, they are not an item of worship as the Supreme Being, creator, maintaner, destroyer of the worlds.

The mystery of moqui marbles (good picture):
http://www.geocities.com/CapeCanaveral/cockpit/8882/moqui.html

This says it all:
Moqui Marbles: They're a concretion, but how and why they were formed is a mystery. They are found at the base of the Navajo Sandstone and are thought to be 130 to 155 million years old. They are roughly spherical, about 1 1/3 to 2 3/4 inches diameter, but each is different and one-of-a-kind. The shell is of heavy natural iron deposits and the centre is filled with extremely fine, coral colored sandstone (much finer than the surrounding Navajo Sandstone). They're beautiful, unique and thought-provoking .... perfect gifts and conversation pieces.
http://www.roawarehouse.ca/Varieties/moqui_balls.html

Moqui stones for healing powers:
http://www.solemn.com/stones.htm

Moqui marbles for Shamans - Shalagrams for Brahmans:
http://www.rocksandminerals.com/specimens/moqui.htm

Moqui Marbles are so called because they have been found in the ruins of the ancient Moqui Indians of Southern Utah.
http://www.haaga.com/utahmarbles/moqui.htm

Good picture of the iron clad moqui balls:
http://www.anglin.chimayo.com/specimens/moqui.html

Want to purchase some moqui balls - here's your site:
http://www.greatsouth.net/p-M180.html