Sterling Silver Cross Necklace

My Great Great Aunt went to a mine somewhere and found a piece of red jasper and had it attached to a custom made cross necklace some 50-odd years ago. She then gave it to my Great grandmother. She then passed it on to my Mother who has given it to me. It is in very nice condition, made of sterling silver, and red jasper. There are no distinguishing marks that I can find, even looking under a magnifying glass. I would like to know where the jasper could have been found if possible, and the estimated price of it. By the way, the pictures are terrible. they were taken by my cell phone last minute, so don't use them to judge, because they cannot do the necklace justice. Thanks!

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