Guide

Look closerLandscape

Purple and black streaks in beach sand after winter storms

February

The pink-purple and black streaks that show up on some Massachusetts beaches, most often north of Boston, after winter storms are heavy mineral sand, not pollution. The purple is mostly garnet, and the black grains are dark heavy minerals, some of which are magnetic.

Why this time of year

Winter storm waves carry off the lighter quartz sand and leave the heavier garnet and dark grains behind in streaks. In spring and summer, wind blows white quartz sand back over them and the color fades from view.

How to notice it

  1. After a winter storm, walk the open upper beach and look for pink, purple, or wine-red bands and black patches in the sand, often near the base of the dunes, above the normal high tide line. Look from the beach; do not climb the dune face.
  2. Compare dry and damp streaks: the pink grains look darker, almost purple, when wet.
  3. Leave every grain where it is. The streaks are for looking.

Try this with kids: Find a dry streak and a damp streak of the pink sand. Which one looks more purple?

Word to know: “Garnet”: a hard, heavy mineral that is pink to dark red.

Safety

  • Stay off the dunes and back from any steep, freshly cut dune face. Look at the streaks from the beach side; on Parker River National Wildlife Refuge the dunes are closed to the public.
  • Leave the sand where it is. On the refuge, collecting or removing sand, and removing shells or rocks without a refuge permit, is prohibited.
  • Winter surf runs high after storms. Keep to the upper beach, well back from the waves.

Sources

  • wbznewsradio.iheart.comNews report (WBZ, page dated Feb 6 2024, secondary) passing on Massachusetts DCR's explanation. The article's own wording: 'We mostly see the garnet and quartz deposits in winter as storms erode the dunes, leaving the heavier minerals exposed.' In spring and summer, lighter white quartz sand blows back over the dunes and covers the colored sand. DCR is quoted that river-borne minerals end up on barrier beaches 'most commonly north of Boston.' This is the source for the winter timing and the months.
  • bostonglobe.comNews (Boston Globe, Feb 6 2024, secondary): the purple sand on Revere Beach in February 2024 was natural. DCR: 'Its chemical composition is normal except for a high concentration of garnet.' A resident said he had seen it 'especially after storms.' Supports 'not pollution' and the link to storms. Does not mention black sand or magnetite.
  • jeolusa.comElectron-microscope analysis of Plum Island sand by the instrument maker JEOL USA (lab analysis posted on a company blog, undated, about 6 years old). 'The purple color (or more appropriately, pink color) comes from the abundance of almandine-pyrope garnet.' Pink sand looks almost purple when wet. The bands appear 'frequently at the base of the dunes above the normal high tide line.' The magnetic black grains were 'a mix of ilmenite FeTiO3 and hematite Fe2O3'; the nonmagnetic black grains were augite. It does not name magnetite. (The /BLOG/ address 301-redirects here; no post date on the page.)
  • historicipswich.netLocal history blog (secondary). Quotes Sandy Tilton (role not stated): garnet 'is heavier than the white quartz sand, so it doesn't wash away as easily'; 'As the storms erode our dunes & beaches, lots of garnet sand is exposed'; 'In the spring & summer, the winds blow the white quartz sand & easily cover the garnet again.' Supports the sorting mechanism and the seasonal cycle on the North Shore. (The 2023/01/06 address 301-redirects here.)
  • coastalcare.orgGeneral mechanism from Gary Griggs, Distinguished Professor of Earth and Planetary Sciences at UC Santa Cruz (an expert explainer, not about Massachusetts). Denser grains 'are left behind by the large winter waves as they remove the less dense quartz and feldspar.' Black minerals 'such as magnetite, ilmenite, and chromite' can be 'separated from the lighter colored sand by a hand magnet.' Garnet is the source of purple sand at Big Sur.
  • fws.govPrimary (USFWS). Without a special refuge permit, 'removal of natural items - including plants, animals, shells, rocks, driftwood, and bones - is prohibited.' Also: 'The majority of the refuge beaches are closed from April 1st into August to protect nesting plovers.'
  • fws.govPrimary (USFWS). Prohibits 'Collecting, digging, or removing sand, dirt, earth, etc., or any other inorganic materials.' The dunes are closed to the public.

Checked against these sources on November 6, 2026.

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