Lichen stromatolite
From Infogalactic: the planetary knowledge core
Lichen stromatolites are laminar calcretes that are proposed as being formed by a sequence of repetitions of induration followed by lichen colonization. Endolithic lichens inhabit areas between grains of rock, chemically and physically weathering that rock, leaving a rind, which is then indurated (hardened), then recolonized.[1][2]
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