Chert can form in parts of the deep sea where the tiny shells of siliceous organisms are concentrated, or elsewhere where underground fluids replace sediments with silica. Chert nodules also occur in limestones.
Todorokite, (Na,Ca,K)2(Mn++++,Mn+++)6O12•3-4.5(H2O), Pedogna quarry, Villa a Roggio, Pescaglia, Lucca, Province, Tuscany, Italy. Crysral size 0.3 mm. Copyright: Luigi Mattei
Cuivre. Oganja (Onganja), Namibie
Gypsum on Calcite, Sulzkirchen, Main Danube Canal, Upper Palatinate, Bavaria, Germany. Fov 8mm. Collection/Copyright: Georg Prock
Learning Geology: How Do You Describe an Igneous Rock?
Psilomelane (mixture of various Mn oxydes : coronadite, hollandite, etc), Taouz, Er Rachidia, Morocco. Hard crystallized black plate of psilomelane with short stalactitic black psilomelane formations to 9 mm standing upright off the top surface
Igneous Rock Color Texture Key
Lavendulan & Acanthite.
Gems: Minerals that are rare, beautiful and durable.