Most of the known examples of heads and busts of emperors, empresses and deities carved in semi-precious stone (usually white or blue chalcedony) were published by W.-R. Megow, Kameen von Augustus bis Alexander Severus, Berlin, 1987. The series of emperors' busts continued into the 4th Century although heads of Imperial women are rarer. Cf. Megow, op. cit., for a chalcedony bust of Antonia (Megow, E5), a green chalcedony head of Drusilla (Megow, D33) in the British Museum and a similar fragment in the Fitzwilliam (Megow, D34).
The hairstyle of the example above is reminiscent of both Agrippina Major and Minor. For cameos of Agrippina Major cf. Megow, op. cit D13, D14, D15, D16, D17, and for Aprippina Minor B25, B26, and B27.
For sculptural portraits of Agrippina Major cf. K. de Kersauson, Catalogues des portraits romains Tome I, Portraits de la République et d'époque Julio-Claudienne, Paris, 1986, pp. 132-135, nos 60-61. For Agrippina Minor cf. Kersauson, op. cit. pp. 202-205, nos 95-96, and V. Poulsen, Les portraits romains, I, Copenhagen, 1962, pp. 96-99, nos 61-63.