4 x 4 x 1"
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I'm not finding that mark on any other pieces by Minton Hollins so have left off that attribution; if you have a link confirming otherwise please forward and I'll change this.
Based on the photos and information provided, and subject to examination, this is:
An Aesthetic Movement style redware tile
Brown-glazed tile with raised Celtic-relief four-point knot in orange glaze; marked indistinctly on the back M-, 1981
4 inches by 4 inches
CONDITION: minor pitting and glaze losses throughout.
*represents a fair-market value for auction purposes; retail or asking price may vary.