A very attractive openwork plaque, modelled as stylised leaves and flowers, the rose cut diamonds all foiled and in closed back settings.
I am not sure what this piece is from but it is very attractive and looks great as a pendant.
I have added a silver, studded ring  so you can easily add it to a chain.
 
The middle diamond measures about .65 carat with a stone measurer but as rose cut diamonds you get the spread but not the depth. So it is probably more like .35
 
European circa 1880
measures - 73mm x 20mm
weighs - 24g
Excellent condition