676 PROCEEDINGS OF THE NATIONAL MUSEUM. Vol.59. 



zones. Under the microscope ludwigite resembles ilvaite to a re- 

 markable degree, as shown by the misidentification of the Korean 

 material by no less an authority than Koto. Acicular black minerals 

 in contact altered limestones should be critically examined, as lud- 

 wigite is more rationally to be expected in such associations than is 

 tourmaline. Ludwigite may simulate tourmaline in megascopic 

 appearance and boron reaction, magnetite in appearance and^ mag- 

 netic properties, and ilvaite in appearance, solubility in acids, and 

 quantitative optical properties. 



