According to https://en.wikipedia.org/wiki/Pseudomorph:

“In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form (crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced by another. The name literally means "false form". Terminology for pseudomorphs is "replacer after original", as in brookite after rutile.

A paramorph (also called allomorph) is a mineral changed on the molecular level only. It has the same chemical composition, but with a different structure. The mineral looks identical to the original unaltered form. This occurs, as an example, in the aragonite to calcite change.

An incrustation pseudomorph, also called epimorph or perimorph, results from a process by which a mineral is coated by another and the encased mineral dissolves. The encasing mineral remains intact, and retains the shape of the original mineral or material. Alternatively, another mineral may fill the space (the mould) previously occupied by some other mineral or material.”

Check amongst your own minerals and see if you have any. Here are some examples I found:

Chalcedony thought to be after fluorite from Ysterputz, Namibia


Pseudomorph of shattuckite after malachite from Kandesei, Namibia


Malachite after azurite with calcite from Tsumeb, ex TVJ


Quartz epimorph after calcite. Karibib, Namibia 


Goethite after siderite bought near Klein Spitzkoppe, Namibia

Limonite cubes after pyrite can be seen in the rocks near the river when you walk around the mine at Vredendal. Keep a look out next time you go there.

All photos Jo Wicht, unless otherwise credited.

Editing by Duncan Miller.