PLUM ISLAND — As many, but not all, islanders know, Plum Island was named after the beach plum bushes scattered around the barrier island.
But on occasion, patches of plum-colored sand can turn up along the beaches above the high tide mark, leading to confusion and puzzlement about the swirling patterns of purple.
Thankfully, according to employees of a Peabody-based scientific research instrument company who wondered the same thing, the purple sand wasn't caused by pollution or algae or any man-made malady.
Instead, the plum-colored batches arise because of naturally occurring pink sand, which when clumped together and wet, appears purple to the human eye.
Three JEOL USA employees visited Plum Island a few winters ago, hoping to spot a snowy owl on one of the dunes.
But along the way, they found a patch of purple sand. Intrigued and knowing they had the tools necessary to find their own answers, they brought samples back to the lab.
"It was so exciting to do that," one of the visitors, Pam Mansfield of JEOL, said in a phone interview Thursday.
Back in Peabody, they used a scanning electron microscope and energy dispersive X-ray spectrometers to determine the cause, according to Mansfield's blog post.
"When large amounts of fine grained pink is intermixed with a smaller number of darker grains and dampened by rain or sea water the human eye will “see” the sand as a much darker pink to almost purple," the blog post continues. "The two most common pink minerals are rose quartz ... and the solid solution series of almandine and pyrope garnet."
Mansfield said she returned to Plum Island in December to take a photo of plum-colored sand and added it to the original blog post.
She said the post proved to be one of the most popular in her time with the company.
Staff writer Dave Rogers can be reached at email@example.com. Follow him on Twitter @drogers41008.