Strata

Strata is a free 3D picross puzzle game. A block of stone hides a crystal, and you chisel away the rock cube by cube, using number clues on the outside of the block to work out which cubes to keep. It plays in your browser on desktop and mobile, with no sign-up.

How to play

• Goal: remove every cube of rock without touching the crystal, which the game calls the specimen.
• Reading clues: every line through the block has a clue plate where it meets the surface. A plain number is how many cubes in that line are specimen, all in one unbroken run. A ringed number means the specimen is split into two runs with rock between them. A 0 means nothing in the line is specimen, so all of it can go. A face with no plate has no clue, which is not the same as 0.
• Chisel, Lock, Flag: Chisel removes rock, and if you chisel the specimen by mistake it is refused at the cost of a mistake and some time. Lock marks a cube you are sure is specimen. Flag is a note to yourself.
• Mouse and touch: work through the layer grid one flat slice at a time, or tap cubes on the 3D block. Tap a clue plate to settle its line.
• Keyboard: arrow keys move, [ and ] change layer, and C, L and F chisel, lock and flag. Press ? for the full list.

The clues are enough to solve every block without guessing. Pick a tier from Core sample up to Expert when you start.

History

Strata reframes Picross 3D — the Nintendo handheld puzzle that carves a voxel model out
of a featureless block — as a mineralogy dig. The reframing changes more than the
paint: in the original, most faces start blank and a clue only appears once carving
exposes it, so early moves are guesswork rewarded in hindsight. Here every clue plate
is visible from the first move. Carving never reveals a clue; it only relocates one to
a face you can currently see, because the cubes behind it are gone. The puzzle is
solved by reading, not by probing.

Usage Tips

• Five tiers: a Core sample block for a one-or-two-minute dig, then Easy, Medium,
  Hard, and Expert. Expert specimens go through an extra subtractive
  carve pass, so their clues include split runs the other tiers never show.
• Three actions on every cube: Chisel removes rock, refusing harmlessly (at the
  cost of a mistake and time) if the cube turns out to be specimen. Lock marks a
  cube you are sure is specimen and is fully reversible. Flag is a note to
  yourself that changes nothing on the board.
• Tap a clue plate to chord its line: if the rock left in the line matches the
  clue, everything left is locked for you; if your locks already satisfy the clue,
  everything left is chiselled. Chording is only as safe as the marks it acts on.
• Hints cost score. Show a line points at a line with something left to deduce;
  settle a cube does one deduction and places it for you. Undo reverses your last
  action but never refunds a mistake, an elapsed second, or a spent hint.
• If your locks make the dig impossible, the HUD says so plainly — it will never say
  which lock is wrong. Work back from the marks you are least sure of.
• The layer grid is where the puzzle is actually solved, one flat slice at a time.
  The 3D block view is the overview: tap a cube to act on it, or drag across cubes
  to sweep a run of the same action. To turn the block, drag the empty space around
  it, use two fingers, or drag with the right mouse button.
• On a keyboard: arrow keys move, [ and ] change layer, X Y Z pick the
  slicing axis, C L F chisel/lock/flag the selected cube in either view, and
  Shift with the same letter switches mode. 1 2 3 chord the across/down/depth
  line, V switches view, Q/E turn the block and W/S tilt it, U undoes, H
  takes a hint, P pauses. Press ? for the full list; hover over any button to see
  its key.
• Your dig autosaves. Close the tab mid-dig and it picks up exactly where you left it,
  mistakes, hints, and clock included.
• Install it as an app for offline play.

Technical Notes

• Every dig is a seeded PRNG draw, so a seed reproduces the same block, mineral,
  habit, and clue layout deterministically.
• The generator's line solver proves each candidate block solvable by pure deduction
  before it is ever handed to a player — no dig on any tier requires a guess.
• Expert tier is not just a bigger block: it runs the same generator through an
  additional subtractive carve pass on the finished specimen, which is what produces
  the split-run clues unique to that tier.
• One reducer drives both the layer grid and the 3D block view — they read and write
  the same state, so switching views mid-dig never loses a move or a mark.
• The 3D block is rendered with an orthographic camera and instanced geometry, with
  clue plates as unlit materials so they stay legible from any angle without depending
  on scene lighting.

Accessibility

The puzzle is fully playable without sight: every clue, every mark, and every action
lives in the layer grid, which is built from real, labelled, keyboard-reachable
controls start to finish. The 3D reveal at the end of a dig is visual only. It is
never described beyond the specimen's name, its block size, its cube count, and the
score — matching exactly what the win summary already states in text.

Questions

Is Strata free? Yes, with no sign-up.

Does it save my progress? Yes. A dig in progress autosaves in your browser on this device, and finished specimens are recorded in your museum.