antique oval miniature brooch / locket, most likely a late-18th to early-19th century mourning or sentimental brooch.

What you're looking at
    •    Front: a hand-painted miniature portrait (often enamel on copper or ivory substitute), showing a lady in period dress (Georgian / early Regency style).
    •    Construction: gilt brass frame with a glass cover.
    •    Back (opened):
    •    One side: hair compartment / fabric insert (very common in mourning or remembrance jewellery).
    •    Other side: cloth or paper backing used to protect the contents.
    •    Loose oval velvet insert: likely the original backing pad, sometimes removed or replaced over time.

What it was used for

These brooches were worn to:
    •    Commemorate a loved one (mourning jewellery)
    •    Hold locks of hair or personal fabric
    •    Display an idealised portrait rather than a named sitter

They were extremely popular in the Georgian era (c. 1780–1820) and remained common into the early Victorian period.

Materials (important for value)
    •    Frame: gilt brass / pinchbeck (not solid gold)
    •    Painting: enamel or watercolour under glass
    •    Interior: silk, velvet, or hair