001: Rocks and Minerals (Collector's series)

by Paul E. Desautels

Hardcover, 1974



Call number

QE363.8 .D47


Grosset & Dunlap (1974), 159 pages

User reviews

LibraryThing member keylawk
I. Collections - "collecting, appreciating, and studying the minerals is a key to unraveling the fascinating story of the earth itself." [6]

"Some of the big museums come close to an estimated 1,800 species [of all known minerals] described in scientific literature. Of this total only a couple of hundred are commonly found...1,200 a strong challenge...the remaining 200 are so rare that they will probably elude [the collector]." [7]

Reasons for the frequent occurrence of certain species as companions in certain types of mineral deposits? Apatite, with wolframite in the Portuguese tungsten mines. Uvarovite, the chromium garnet, is found with kammererite, the chromium mica. What other pairings can be predicted?

Commercial value of a collection - assess the value of the ore, the mineral's chemical composition, form, rarity, beauty, color, size, hardness, uniqueness, combination with native elements, and mineral associations. How coveted by the connoisseurs.

GOLD - Smithsonian has an 82-ounce nugget from California.

SILVER - sculptured masses of twisted wire and crystal groups from Kongsberg, Norway.

COPPER - Keweenaw Peninsula in Michigan, and Ajo, Arizona, in masses of several hundred tons, and crystals or fern-like fronds.

SULPHUR (Sicily) and DIAMOND (S.Africa - 254-carat in Smithsonian is largest uncut crystal on record) supply the best specimens of nonmetallic elements.

SULPHIDES/ SULPHOSALTS - stibnite (Shikoku), galena (Missouri), bournonite (Cumberland England), the "ruby silvers" (proustite and pyrargyrite) are blackened by light, cinnabar, realgar (altered chemically to orpiment), Argentite, millerite, tetrahedrite, pyrite, arsenopyrite, chalcocite, etc.

HALIDES - natural salt. Halite is soft and altered by humidity. Fluorite is excellent to collect -- shades of blue, green, purple, tan, gray, yellow, colorless, amber! Atacamite (Australia), boleite and cumengite (lead-copper-silver chlorides from Baja California).

OXIDES - Some major gem minerals are among the oxides: corundum (both ruby and sapphire), spinel, chrysoberyl (the only one occuring in an appealing natural specimen). Hematite (common iron ore, called "kidney ore" in England), rutile (source of titanium), cassiterite (Bolivia), anatase, cuprite, spinel, franklinite, etc.

CARBONATES - Calcite (often paired with copper carbonates asurite and malachite), asurite, rhodochrosite, smithsonite (a zinc carbonate), witherite, malachite (Congo/Zaire), cerussite, siderite, aragonite, etc.

SILICATES - most of the world is silicate mineral. Big Trio, all with a series of colors: (1) Tourmaline (elbaite rediscovered near Pala, and shiny black crystals called "schorl" from New York, and brown ones called "dravite" from Australia); (2) Topaz; (3) Beryl - emerald, morganite (paired with elbaite in San Diego County), mostly from Minas Gerais Brazil, epidote (Alaska and Australia), ilvaite, datolite, danburite, axinite, etc.

OTHER MINERAL GROUPS. Molybdates, phosphates, arsenates, borates, etc. Note the legrandite and adamite (zinc arsenates) coming out of Mexico in large quantities.

Photographs of specimens from the Smithsonian are included "to leave a strong impression of the subtle qualities that are possessed by all fine mineral specimens". [16]

II. COLLECTING. "An unassorted, disarranged, unlabeled pile of pebbles is not a 'collection'. It is merely gravel." [146 - sounds familiar!]

MINERAL STUDY - how do we recognize, sort, and differentiate mineral species? By their chemical and crystallographic composition. Reference, James Dwight Dana (Yale) SYSTEM OF MINERALOGY (1884).

(1) Hardness. Represented by ten well-known minerals representing degrees: {1}talc {2} gypsum, {3} calcite, {4} fluorite, {5} apetite, {6} feldspar, {7} quartz, {8} topaz, {9} corundum, {10} diamond.

2. Tenacity. (Ex. Jade is soft but holds together; topaz is hard but shatters).

3. Cleavage. Breakage pattern. "Fracture" if jagged/irregular. "Parting" if predictable. Graphite cleavage in one direction, so easily, makes it a lubricant.

4. Growth Pattern. Crystals may be "acicular", "bladed", "tabular", "pyramidal", capillary, "arborescent" (dendritic), "botryoidal" (grape-like), "mammillary", or "reniform", etc. Asbestos is fibrous. Aragonite is coralloidal (twisted, tangled). Etc.

4. Luster. {color}-metallic, greasy, pearly, glassy or vitreous, silky, dully, splendent, glistening.

5. Diaphaneity. Amount of transparency, to opaque.

6. Streak. The color when powdered, or on a streak plate.

7. Fluorescence.
8. Magnetism.
9. Color. Idiochromatic or allochromatic (variable). Sulphur is id. and always yellow. Beryl is al. and may be colorless, green, blue, pink, red, or yellow.

10. Specific Gravity. Requires chemical apparatus and arithmetical ability.

11. Index of Refraction. Requires apparatus. refraction bending of light through the sample.

12. X-Ray Examination.
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159 p.; 11 inches


0448115409 / 9780448115405


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