Spiky Growth

From Softology's collection · B13,17,20-26/S0-3,7-9,11-13,18,21-22,24,26/C4

Noise hardens into spiky clumps within a few generations.

How the rule works

Each cell has 26 neighbours: every cell that shares a face, an edge or a corner with it (the Moore neighbourhood).
An empty cell comes alive when 13, 17 or 20 to 26 of its neighbours are alive.
A live cell stays alive when 0 to 3, 7 to 9, 11 to 13, 18, 21, 22, 24 or 26 of its neighbours are alive; otherwise it starts dying: for 2 generations it fades, is not counted as a neighbour and blocks births, then the cell is empty again.
With 4 states in all (alive, 2 dying, dead), this is a Generations rule.

It starts from a random fill with 15% of cells alive.

B lists the neighbour counts at which an empty cell is born, S those at which a live cell survives, and C the number of states. How to read a rule