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This is a nice king Charles Ist silver Half Merk (6 shillings 8 pence). Second (Briot's hammered) coinage Edinburgh 1636 AD.
Obverse profile bust of Charles with VI over 8 behind: · CAROLVS D G SCOT ANG FR & HI REX (Charles, by the Grace of God, King of Scotland, England, France and Ireland)
Reverse: Crowned shield of arms within, legend around CHRISTO AVSPICE REGNO (I reign under the auspice of Christ)
DENOMINATION: Half Merk
CULTURE: Stuart Scotland
MONARCH: King Charles I
DATE: 1625 - 1649 (this coin minted in 1636 AD)
SIZE: 26mm diameter
WEIGHT: 3.02 grams
ATTRIBUTION: Spink 5546
PROVENANCE: Formerly in a private collection, Inverness, Scotland.