Derby — Occurrence of Monazite in Iron Ore, etc. 211 



Art. XIX. — On the Occurrence of Monazite in Iron Ore 

 and in Graphite ; by Orville A. Derby. 



A small specimen of magnetic iron ore presented by Mr. 

 John Gordon of Rio de Janeiro, from the fazenda Catita, on 

 the lower Rio Doce in the state of Espirito Santo, presents a 

 number of interesting features, among which is the occurrence 

 of numerous and comparatively large grains of monazite in 

 the mass of the ore. The ore fragment consists of a coarsely 

 crystalline mixture of magnetite and ilmenite with adherent 

 remnants of kaolinized feldspar and biotite, which show it to 

 have been a segregated mass of oxides in the midst of a 

 coarsely granular rock, probably a mica-syenite. The pow- 

 dered ore, freed from the iron oxides by the horseshoe and 

 electro-magnet, gives an extremely abundant residue of rather 

 coarse fragments and well crystallized grains of corundum, 

 monazite and zircon, and in microscopic slides these grains are 

 found to the number of a dozen or more in the area of an 

 ordinary preparation. They occur isolated in the mass of the 

 oxides, but are more abundant in and about flakes of biotite 

 when these are present. Of the three minerals, monazite is the 

 most abundant and the most generally distributed, appearing in 

 both the magnetite and ilmenite. Other interesting accessories 

 that are confined to the magnetite, where they appear as deli- 

 cate net-like partings in the twinning planes (something like 

 the plates of tsenite in meteoric irons), are a green spinel and 

 a translucent brown titanium mineral. The ilmenite also gives 

 on etching irregular bands showing it to be composed of a mix- 

 ture of two substances of different color, and degree of solu- 

 bility in hydrochloric acid. This and other interesting features 

 of titaniferous iron ores from this and other localities will be 

 more fully discussed by Dr. Hussak. 



A specimen of graphite has recently come to hand from the 

 region of the river Jequitinhonha in the state of Minas Geraes, 

 which gives on washing a very abundant residue of heavy yel- 

 lowish fragments, rarely crystals of recognizable form, that on 

 microscopic and chemical examination prove to be monazite 

 and zircon, the former greatly predominating. The only other 

 recognizable element of the residue is a dirty white opaque 

 titanium mineral that seems to be a pseudomorph after mica. 

 The compact graphite is transversed by thin stringers of a 

 decomposed micaceous mineral which also occurs in small iso- 

 lated rounded patches, but these afford no more, if as much, 

 monazite as the purer portions of the specimen. Several iso- 

 lated flakes of graphite with an included grain of monazite 

 were obtained. From the rarity of perfectly formed crystals 



