The crystal structure of lizardite-1T from Gew-graze, Cornwall, has been refined by single-crystal X-ray diffractionto R1 of 0.0263 and 0.0557, for two crystals having P31m space group and lattice parameters a = 5.2905(5) Å, c = 7.2815(8) Å, and a = 5.3111(10) Å, c = 7.2907(15) Å, respectively. The Gew-graze lizardite is very close to the end-member composition, so these refinements confirm the existence of well crystallized pure Mg-lizardite and show this to be the most weakly H-bonded lizardite ever refined. With regard to its lattice parameters, Si–O bond distances and geometrical parameters controlled by interlayer interactions (i.e. H-bonding), the Gew-graze Mg end-member lizardite yields slight but observable geometrical differences compared with previous refined structures for specifically, aluminous, lizardites.

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