162 Pyrites investing Quartz, &e. 
in which these minerals usually occur,) indicate the existencé 
of trap rocks in those islands ;—Laumonite, Calcedony, 
Prehnite and Stilbite, in transparent flesh colored crystals, 
and in compact brick red masses. 
Crystals of quartz, in portions of large geodes, and most 
of the specimens indicating that they formed either imbedded 
masses or veins. Cc. U.S. 
VII. Pyrites investing Quartz, Vegetable Stalks, e.; 
in a letter from Mr. Lucius Lyon, dated Detroit, Mich. 
Ter. Sept. 7, 1826.—We have reeeived specimens of a min- 
eral which, “ by rabbing against any hard substance, or even 
woollen, or cloth of any description, acquires a strong yel- 
lowish resinous lustre, which led the Indians, who first observ- 
ed it, to suppose it was gold, and they were accordingly very 
cautious abont discovering the place where it was found. It 
was sent to Mr. Lyon for examination, by Col. Boyd, U. 5. 
ent for Indian affairs, at Mackinac, and is found on the 
river Marquette, in the north-western part of the peninsula of 
Michigan. It is said to be abundant.” 
‘¢ Before the blow-pipe it burns for a short time with @ 
bluish flame, and yields a slight odour of sulphur; the 
smaller particles decrepitate, and it is difficultly fusible by it- 
: with borax, melts easily into a bluish glass.” 
In addition to the above observations, contained in Mr. 
Lyon’s letter, we will mention, that this mineral is not mag- 
netic, but becomes decidedly so after being heated red hot on 
charcoal. Its colour, before heating, is a delicate and beau- 
tiful bronze ; it becomes black by heat, and then ceases te 
emit the sulphurous odour. 
This mineral occurs in the specimens sent, for the most 
part, in the form of minute rounded ovoidal (not angular) 
asses, of the size and shape of a common small written ©, 
and from that up to the dimensions of a capital O. On be- 
ing broken, they are found to be composed of quartz, with a 
very thin coating of iron pyrites—in general not thicker than 
foolscap paper, but still the coating is perfect, and leaves n° 
part of the stone uncovered. Among these minute pebbles, 
are eae see vegetable stalks, not larger than a common 
pm, and they also are completely invested by the pyrites, S° 
that their broken ends, and the eich icone tapes ‘rough- 
ness of their surfaces, are exactly copied by this delicate min- 
eral drapery. When these small sticks are broken, the py- 
