Neotocite, also known as Penwithite, is similar in composition to Serpentine and is an alteration product of Bementite. The chemical formula of Neotocite is (Mn2+Fe2+)SiO3 · H2O (Hydrated Manganese Iron Silicate) and its molecular weight is 149.26 gm. It is not a scarce mineral but rarely available as a faceted gem. Neotocite is always opaque and usually a shade of liver brown. Moh’s Hardness of Neotocite is 3.0 – 4.0.

Neotocite is found in many locations worldwide including Mitterdorf, Styria, Austria; Mont Saint-Hilaire, Rouville County, Québec, Canada; Valgraveglia Mine, Reppia, Graveglia Valley, Ne, Genova Province, Liguria, Italy; Noda-Tamagawa mine, Iwate Prefecture, Tohoku Region, Honshu Island, Japan; Lovozero Massif, Kola Peninsula, Murmanskaja Oblast’, Northern Region, Russia; Harstigen Mine, Pajsberg, Filipstad, Värmland, Sweden; and Franklin, Franklin Mining District, Sussex County, New Jersey, USA. 


Chemical Formula: (Mn2+Fe2+)SiO3 · H2O
Hydrated Manganese Iron Silicate
Molecular Weight: 149.26 gm
Manganese 27.60 % Mn 35.64 % MnO
Iron 9.35 % Fe 12.03 % FeO
Silicon 18.82 % Si 40.25 % SiO2
Hydrogen 1.35 % H 12.07 % H2O
Oxygen 42.88 % O
  100.00 % 100.00 % = TOTAL OXIDE


Crystallography: Amorphous
Crystal Habit: No crystals since it is Amorphous
Twinning: None


Cleavage: None
Fracture: Conchoidal
Tenacity: Brittle
Moh’s Hardness: 3.0 – 4.0
Density: 2.1 – 2.7 (g/cm3)
Luminescence: None
Radioactivity: Not Radioactive


Color: Black, dark Brown, liver Brown, Olive Green
Transparency: Opaque, Translucent in thin fragments
Luster: Dull to Resinous or Vitreous, may be slightly metallic
Refractive Index: 1.50 – 1.65  Isotropic
Birefringence: 0.00 (Isotropic)