Carborundum Crystal Detector

Marble based carborundum crystal detector by the Long Distance Wireless Instument Company. 

Invented in 1906 by Henry H. C. Dunwoody, this consisted of a piece of silicon carbide (SiC, then known by the trade name carborundum), either clamped between two flat metal contacts, or mounted in fusible alloy in a metal cup with a contact consisting of a hardened steel point pressed firmly against it with a spring. Carborundum, an artificial product of electric furnaces produced in 1893, required a heavier pressure than the cat whisker contact.The carborundum detector was popular[ because its sturdy contact did not require readjustment each time it. was used, like the delicate cat whisker devices.

Here you find 4 models, 4 with images and 0 with schematics for wireless sets etc. In French: TSF for Télégraphie sans fil.
All listed radios etc. from Long Distance Wireless Instrument Company; Boston, MA