Removing Matrix

After preliminary cleaning of the fossil, bits of matrix may still mask important details. Removal of these pieces to aid identification and create a more attractive display specimen requires skill and infinite patience. It takes at least an hour to clean a small trilobite which has soft, relatively easy-to-remove shale embedded between its ribs. It may take days to clean a limestone slab with many crinoid crowns.

The principle behind cleaning matrix from a fossil is to exploit the difference in hardness between fossil and matrix, or, if acid is used for cleaning, the difference in chemical composition. Even though a fossil replaced by calcite is embedded in limestone (also calcite), there seems to be a slight difference in hardness between the fossil and matrix, particularly after some weathering. The calcite grains of matrix, moreover, do not have a close bond with the calcite crystals of the fossil, so that there is a plane of weakness between fossil and matrix.

Softer matrix can be brushed or scraped away or flaked off along the plane of weakness. This is easy if the fossil is composed of a very hard substance (such as pyrite or quartz) and the matrix is something soft (such as shale). It is more difficult when calcified fossils are embedded in limestone. It is nearly impossible when a soft fossil (such as a bone) is in hard matrix (such as limestone).

0 0

Responses

  • alvise
    How to remove a fossil from matrix?
    5 months ago
  • swen
    How to remove matrix from Calcite?
    16 days ago

Post a comment