Cartier, an Art Deco rutilated quartz and diamond desk seal

Cartier, an Art Deco rutilated quartz and diamond desk seal, circa 1913, modelled as a plinth in polished rutilated quartz, accented with rose-cut diamonds, the seal engraved with a ducal and a royal coat of arms, signifying the marriage between Archduchess Mechthildis of Austria (1891 - 1966) and Prince Olgierd Czartoryski in 1913, measuring 6.5 x 2.4 x 2.4cm, signed Cartier Paris Londres New York, faintly numbered, French assay mark