Two years ago this month, Larry R. Couture took a walk on the beach in Aquinnah and spotted something shining in the sand. He found a piece of clear crystal quartz the size of a tennis ball. Though he didn’t know it at the time, it was a rare find.

This summer, Mr. Couture returned to the Island carrying a 60-carat quartz crystal. The gem was cut from the stone.

Mr. Couture, 51, of Bellerica, is a health insurance professional. He has been coming to the Vineyard every summer with his family since the 1970s. He fishes and spends a lot of time at the beach. Two years ago the family went to Philbin Beach for the day and he started walking toward the cliffs with his son late in the afternoon.

“I am always looking for stones, pieces of pyrite, fool’s gold. I look for stones that are reflecting sunlight. I found this stone. It glowed like a headlight in the sand,” he said. He does not claim to have any expertise in stones. He said he found the stone a few feet up above the high water mark.

Mr. Couture recalled a day of fishing barefoot at Lobsterville beach when he was 17. “I got an old shark’s tooth into my foot. I cut myself so deeply, it required stitches,” he said.

Quartz is a common stone in New England. There is plenty of white quartz around. At times when quartz is found clear, it has lots of impurities in it. This stone is different. To find one so large and so pure on the Vineyard is rare. Even more unusual is that a gem cutter could produce such a large size gem. The gem is 22 by 22 by 19 millimeters.

Phil McCrillis of Plumbago Mining Corp. in Greenwood, Me., is one of the top gem cutters in New England. A fourth generation Maine gemstone miner, he cut the stone.

Reached by telephone, he said he believes Mr. Couture’s find is valued at $3,000. And he said what distinguishes this stone from others is not just what it is made of but where it was found.

The Vineyard was created by deposits of sand and stone debris left behind by receding glaciers thousands of years ago. Mr. McCrillis wondered whether the stone might have come here from the ballast of a ship. “I didn’t see any glacial wear and tear,” he said.

For Mr. Couture the stone is a wonder and a find that has taken him down a road of discovery and meeting interesting people. “I got a call from Smithsonian and another more local museum, shortly after I picked up the stone,” he said. He has been asked to donate the stone, but he has another idea.

“I would like to have this piece viewed on the Vineyard,” he said. “I think ideally it should be here on the Island.”