Red Oxide of Copper--This rather rare mineral is found in small quantities in this mine, or near it, in the debris or outcrop. Perfect crystals, which are of a dodecahedral or octahedral form, are fairly abundant. They are difficult to distinguish, as they are generally coated, or soiled at least, with malachite. The color proper is of a brownish red, and the hardness about 4, although sometimes, it is earthy, with an apparent hardness not over 2. The crystals are generally about a quarter of an inch to a half of an inch in diameter, and found inside the masses of malachite. When these are broken open, the red copper oxide is readily distinguished, and may be separated or brought into relief by carefully trimming away the malachite surrounding it as its gravity (6) is much greater than malachite. When a piece of the last is found which has a high gravity, it may be suspected and broken into, as this species is much more valuable and rarer than the malachite which is so abundant. It dissolves in acids like malachite, but without effervescence, if it be freed from that mineral, and acts the same before the blowpipe. Sometimes it may be found as an earthy substance, but is difficult to distinguish from the red sandstone accompanyit, which both varieties resemble, but which, not being soluble in the acids, find having the blowpipe reactions, is thus characterized. This red oxide of copper does not form a particularly showy cabinet specimen, but its rarity and value fully compensate for a search after it. I have found considerable of it here, and seen some little of it in place remaining.
Chrysorolla.--This mineral, very abundant in this locality, resembles malachite, but has a much bluer, lighter color, without the fibrous structure so often present in malachite, and seldom in masses, it only occurring as light druses and incrustations, some of which are very beautiful, and make very fine cabinet specimens. Its hardness is less than that of the other species, being under 3, and a specific gravity of only 2, but as it frequently occurs mixed with them, is difficult to distinguish. It does not dissolve in nitric acid, although that takes the characteristic green color of a solution of nitrate of copper, as from malachite or red oxide. This species is found all over this locality, and a fine drused mass of it will form an excellent memento of the trip.
Copper Glance.--This mineral is quite abundant in places here, but fine crystals, even small, as it all is, are rare. That which I have seen has been embedded in the loose rock above the mine, about a quarter inch in diameter, and more or less disguised by a green coating of chrysocolla. The color of the mineral itself is a glistening grayish lead color, resembling chromite somewhat in appearance, but the crystals of an entirely different shape, being highly modified or indistinct rhombic prisms. The specific gravity is over 5, and the hardness 4. Before the blowpipe on a piece of wood charcoal it gives off fumes of sulphur, fuses, boils, and finally leaves a globule of copper. In nitric acid it dissolves, but the sulphur in combination with it separates as a white powder. A steel knife blade placed in this solution receives a coating of copper known by its red color.
Erubescite--This mineral occurs massive in the rock here with the other copper minerals, and is of a yellowish red color, more or less tarnished to a light brown on its surface, Before the blowpipe on charcoal it fuses, burns, and affords a globule of copper and iron, which is attracted by the magnet. Its specific gravity is 5, hardness 3. It resembles somewhat the red oxide, but the low gravity, inferior hardness, lighter color, and blowpipe reaction distinguish it. These are the only copper minerals likely to be found at this mine, and the following table and note will show their characteristics:
Name. Speci- Hardness Action of Action of Color. Form.
fic Blowpipe Heat. Hot Nitric
Gravity. Acid.
Mala- From 4 From 3 Decrepitates, Dissolves Pure Oil Fibrous,
chite to 4.5 to 4 but fuses with with Green. massive,
borax to a effer- or in-
green bead. vescence crusting.
Red 6 From 3.5 On charcoal Dissolves A deep Modified
Oxide to 4 yields a without brownish crystals.
globule of effer- red.
copper. vescence
Chryso- From 2 From 2 Infusible. Partly Bright Incrus-
colla to 2.3 to 3 soluble bluish tations.
green.
Copper 5 From 2.5 Fumes of Copper Grayish Modified
Glance to 3 sulphur and a soluble, Lead. rhombic
globule of sulphur prisms.
copper deposits
Erube- 5 From 3 Fumes of Partly Yellowish Massive.
scite to 3.5 sulphur and soluble red or
magnetic tarnished.
globule.
Malachite is characterized by its color from Copper Glance and Red Oxide and Erubescite, and from Chrysocolla by the action of the acid, the fibrous structure and blowpipe reaction, gravity, and hardness.
Red Oxide is distinguished from Erubescite, which it alone resembles, by its darker color, higher specific gravity, and yielding a globule of pure copper.
Chrysocolla is characterized by its low specific gravity, light color, lack of fibrous structure, blowpipe reactions, and the acid.
Copper Glance is distinguished by its color, fumes of sulphur, and globule of copper.
Erubescite is distinguished from Red Oxide, which it alone resembles, by its lighter color, great solubility when pure, and yielding a magnetic globule before the blowpipe in the hollow of a piece of wood charcoal, which is used instead of platinum wire in this investigation.