Navajo ring getting stuck on magnet

Tested this ring for sterling and it was positive but its get stuck to the magnet only around the stone area. another thing this looks real old any idea what this ring is worth or how old it is.

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The ring does have some age, impossible to get an exact date but would put it between 30 - 40 years old. If we had a ring like this it would retail somewhere around $60. The backing on the piece of turquoise has iron filings to increase the weight, you always here stories about old time traders taking a magnet over a group of stones someone wanted to sell them, they never seemed to think to highly of the seller when the magnet picked up the turquoise.