todorokite it is nearly 0.02. Todorokite is distinctly pleochroic, appearing dark brown when viewed along the X direction, and yellowish brown when viewed along the Z direction [3], but the strength of the effect varies from faint to strong in material from different localities. The orientation of optical directions with respect to the lattice parameters is Y parallel to b and Z near or parallel to c. Physical properties Todorokite has perfect cleavage parallel to the plane containing the b and c axes, and parallel to the plane containing the a and c axes. Contact twins occur frequently. The mineral is very soft, with hardness only . It is generally fibrous, making it difficult to measure the specific gravity accurately. The Berman balance measures the relative weights of the specimen in air and in water; when todorokite was tested in this way it gave a value of 3.49. The pycnometer measures the mass and the volume of the specimen directly; this method gave a value of 3.66 to 3.82 for todorokite. The pycnometer is more likely to give an accurate reading for a fibrous material. Solubility Todorokite is soluble in hydrochloric acid (HCl) with the evolution of chlorine (), and in concentrated sulfuric acid () forming a purple-red solution. It is also soluble in nitric acid () forming a residue of manganese dioxide (). Other characteristics When todorokite was first discovered, in 1934, modern methods of mineral analysis were not available, and one of the standard techniques was to use a blowpipe to heat a small sample of the mineral, and observe its behavior. Todorokite was tested in this way, and it was noted that under the blowpipe it turned brown and lost its metallic luster, but did not fuse. X-ray diffraction lines at 9.5 to 9.8 Å and 4.8 to 4.9 Å are characteristic. This is also true of buserite . Type locality The type locality is the Todoroki mine, Akaigawa Village (25 km SW of Ginzan), Shiribeshi Province, Hokkaido, Japan. Type material is conserved at the Harvard Mineralogical Museum, Cambridge, Massachusetts, US, reference 106214. Occurrence and associations Although todorokite is a common product of oxidation and leaching of primary manganese carbonate and silicate minerals, its major occurrence is in deep-sea ferromanganese nodules. Todorokite has been synthesised from birnessite in the laboratory, and it is possible that most natural todorokite is derived from birnessite. At the type locality in