Mochi Tetsu

[piryohae3]

I found this website that says Japan had another iron source called mochi tetsu that was high quality, easier, and cheaper to use than satetsu. 

 

http://gunbai-militaryhistory.blogspot.com/2018/02/iron-and-steel-technology-in-Japanese.html

 

He refers to this source: Origin and development of iron and steel technology in Japan by "Kenichi Iida

 

The author says it's found in large quantities in modern day Iwate region. Anyone know how common mochi tetsu usage was in the past?

[ROKUJURO]

Iron oxides are generally known to form minerals of ball or bulb shapes, so MOCHI TETSU might mean just that (in USA: Moqui marbles). If in IWATE/Japan it was an ore with high iron content, it was perhaps bean ore (pisolitic iron ore). In earlier times, it might not have been known to the Japanese that it was an iron ore, or it was not found on the surface like SATETSU and had to be mined. 

[TomBell]

Mochi Tetsu is high purity magnetite (Fe₃O₄) ore.  It's origin is from a skarn deposit formed where an intrusive igneous body ("granite") makes contact with limestone.  The Kamaishi mine in Iwate Province is the largest known copper-magnetite skarn in Japan.  This deposit has been mined from the Tokugawa shogunate until the mine closed within the last couple of decades.  Alluvial mining in the surrounding drainages probably predated the underground mining.

 

Mochi Tetsu ore originated from these deposits as they were eroded.  The magnetite ore fragments were tumbled into rounded cobbles, gravel and sand in the steep drainages that surround these deposits.  The larger pieces could be easily recognized in the alluvium due to their density, color and magnetism.  Smaller magnetite grains can be separated from less dense mineral grains by gravity methods like panning or sluicing.  

 

Like alluvial diamonds or gold, impure lumps of magnetite ore would be more easily broken up during sediment transport resulting in a natural beneficiation process that raised the grade from the 30% iron in the ore body to ~60% iron.

 

Satetsu ore probably originates from skarns as well but has been transported farther from the source.  This reduces the magnetite ore to its constituent crystals by abrasion and collisions with other grains in the streams that carry it to the coast.  Wave action on beach fronts works as a gravity separation process concentrating it into thin black layers in the beach sand.

[ROKUJURO]

Thank you Tom,

that is a good explanation!

[Rivkin]

There have been multiple attempts in pre-Meiji times to use iron ores, but surprisingly the literature asserts that until Ansei at least iron sand and tatara accounted for >95% of steel produced. The shift to iron ore and blast furnace was part of modernization effort and came later.

[TomBell]

Magnetite is commonly the primary iron mineral mineral in black sands around the world.  In the geologically recent terrain of Japan, skarns would be a significant but not exclusive source of magnetite for iron sand.  Masa iron sand which contains magnetite appears to be the feed stock for tatara production of small batch steel.  From what I can tell, akome iron sand which has a bit of titanium in the magnetite was used as a flux to start the initial melt in the tatara or was used to produce pig iron.

 

There is another potential source of iron that has been recognized since the Iron Age which is known as bog iron ore.  This forms when ferrous iron in oxygen depleted groundwater is subsequently oxidized to ferric iron by bacteria in a swamp.  This is a low grade source of iron but was widely used to make pig iron in antiquity and even during colonial times in North America.  The primary iron minerals are hydrated iron oxides which when dehydrated form hematite (Fe₂O₃).  Self fluxing hematite ores are now the primary feedstock for modern steel production.

[Ken-Hawaii]

Excellent info - thanks!

[TomBell]

I ran across this excellent narrative of the tatara smelting process.  My interpretation of the use of akome iron sand is partially wrong.  It seems it was used exclusively to produce pig iron.

 

My points about the origin of mochi tetsu however still add context to the original question posed by piryohae3.  The streambeds below Kamaishi must have been of great value to the local economy.