I have found out that this object is a branch of two oranges, with their leaves, covered in a calcium crust. This mineral would have been made by placing the oranges in the waters of Carlsbad in the Czech Republic over 200 years ago. Count de Bournon wrote about this item in his c1799 catalogue:
"Incrustation de Spath calcaire, faite sur un bouquet de feuilles d'oranger aux quelles étoient adhérentes deux oranges, placé dans les eaux incrustantes de Carlsbad en Bohême une cassure faite, sur le milieu de la réunion des tiges, laisse appercevoir que cette incrustation Spathique, qui est d'un rouge brun foncé à texterieure, est d'un jaune ocreux dans l'intérieur".
Which translated reads:
"Incrustation of calcareous spar, made on a bunch of orange-tree leaves to which two oranges were attached, placed in the encrusting waters of Carlsbad in Bohemia. A break, made on the middle of the junction of the twigs, allows one to see that this sparry incrustation, which is a dark brown red on the outside is yellow ochre inside."
Apparently, it was a common for people to put things in petrifying springs like this to see how long they took to become 'petrified '. It would take approximately two years for such objects, which were then available for sale to visitors there...