the berk
know what you're holding
the field guide
great lakes rocks & fossils · by rarity
The stones on this beach have been hundreds of millions of years in the making — some of them billions — and some walks, you pull a one-of-one. Here's how to know when you have.
★★★★★grailthe 1/1s — a find people will drive to see
chlorastrolite
mineral · state gem"greenstone" — segmented turtle-back pattern, chatoyant green
keweenaw beaches · never take from isle royale
copper replacement agate
mineralagate banding shot through with native copper metal
keweenaw peninsula
trilobite (whole)
fossilsegmented three-lobed arthropod, ~400 million years old
quarries & lucky gravel — beach whole = legendary
datolite nodule
mineralporcelain-smooth nodule; copper tints it pink, orange, white
keweenaw copper country
★★★★ultra rarechase stones — the reason you keep walking
lake superior agate
mineralconcentric banding, carnelian reds — "eyes" multiply the prize
superior shores, west u.p.
thomsonite
mineralpink-green radiating "eyes" in dark basalt
grand marais & keweenaw
yooperlite
mineralplain gray by day — blazes orange under UV light at night
lake superior · bring a blacklight
amethyst
mineralpurple quartz points, often in vein fragments
lake superior shoreline pockets
leland blue
industrial-era glassblue smelter slag from 1870s iron furnaces — history, not geology, and prized anyway
leland & nearby shores only
★★★rarethe frame-worthy finds
petoskey stone
fossil coralhexagonaria — six-sided chambers, each with an "eye"; wet it to see
nw lower peninsula · common near petoskey, rare elsewhere
charlevoix stone
fossil coralfavosites "honeycomb" — like a petoskey but tiny, tight cells, no eyes
charlevoix & lake michigan shores
horn coral
fossilrugosa — a curved horn with ridged growth lines
statewide gravel & shores
pudding stone
rockwhite quartzite studded with red jasper pebbles — carried down by glaciers
drummond island & eastern u.p.
lightning stone
concretionseptarian — gray stone webbed with pale mineral "lightning" cracks
southern lake michigan shores
jaspilite
rockbanded iron — red jasper striped with silver hematite, 2 billion years old
marquette iron country
mary ellen jasper
fossil · stromatolitedeep-red jasper of ~2-billion-year-old algae domes — the organisms that gave earth its oxygen
minnesota iron range*
★★uncommongood eye — most people walk past these
crinoid stems
fossil"michigan cheerios" — tiny stone rings from sea-lily stalks
everywhere limestone is
chain coral
fossilhalysites — loops linked like tiny chains across the surface
statewide shores & gravel
brachiopod
fossilribbed fan — a shell-shaped marine animal, not a shell (we checked)
statewide
banded chert
rockwaxy, layered bands; rings when tapped
statewide gravel
unakite
rockpink feldspar mottled with green epidote — altered granite
lake superior beaches
★commonevery walk — and where every collection starts
quartz pebble
mineralglassy white, glacier-tumbled smooth
every beach
granite
rocksalt-and-pepper speckle — canadian shield, delivered by ice
every beach
basalt
rockdark, dense, satiny — old lava, skips beautifully
every beach
fossil hash limestone
fossilgray stone crowded with broken bits of everything above — a starter pack in one rock
every beach