ROMANECHITE
Here's a sample of botryoidal psilomelane.
This term no longer applies to a mineral. Psilomelane turns out to be
masses of different manganese oxide minerals. However, the dominant
mineral in such specimens is romanechite, a barium manganese
hydroxy-oxide (BaMn+2Mn+48O16(OH)4).
Romanechite has a nonmetallic to “submetallic” luster
(I don't see the latter in available materials), a dark gray to black color
& streak, is moderately hard (H=5 to 6), and has no cleavage. It
forms fine-grained masses without visible crystals. Romanechite often
occurs as botryoidal masses (seen in cross section on sample below).
Romanechite (field of view 3.9 cm across) makes up most of this botryoidal
mass called psilomelane. Other minerals known to be present in
psilomelane rocks are cryptomelane (potassium manganese oxide - KMn8O16),
manjiroite ((Na,K)Mn8O16·nH2O), and todorokite
((Mn,Ca,Mg)Mn3O7·H2O).