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Assay Lab Resources

A reactant or reagent is a substance consumed during a chemical reaction. The reaction process always results in the interconversion of chemical substances.

The wet reagents listed below are useful in determining the major elements present in a given specimen, and serve as aid in mineral identification.

Dana's Manual of Mineralogy

Edward S. Dana

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Water: H2O; distilled water is preferred in all assaying experiments (pure rain water actually works quite well)

Hydrochloric Acid: HCl; a.k.a. “muriatic acid”; both concentrated and dilute solutions are required in the laboratory; concentrated solutions of 12 M HCl can be easily diluted by mixing with distilled water; (remember to always add acid to water rather than the reverse); HCl is used to precipitate chlorides of silver, lead, and mercury from nitric acid solutions

Nitric Acid: HNO3; a.k.a. “aqua fortis”; again, both concentrated and dilute solutions are used in assay work

Ammonia: NH3; a strong base used to precipitate hydroxides of aluminum, beryllium, bismuth, chromium (III), iron, lead, and titanium from acidic solutions containing those metals

Hydrogen Peroxide: H2O2; a strong oxidizing agent used in some tests f. nitrohydrochloric acid: HCl and HNO3; a.k.a. “aqua regia” and “royal water”; consists of 3 parts HCl and 1 part HNO3; it is the only acid capable of dissolving gold and the other noble metals

Sulfuric Acid: H2SO4; a.k.a. “oil of vitriol”; both concentrated and dilute solutions are used in the assay lab; sulfuric acid is used to precipitate sulfates of lead, barium, and strontium from weak acidic solutions containing HCl and any of the above metals

Ammonium Hydroxide: NH4OH; a strong base used to dilute the strong acids

Potassium Hydroxide: KOH; a.k.a. “caustic potash”; an extremely strong base used to neutralize the strong acids and to confirm the presence of aluminum hydroxide when employing the ammonia test for aluminum

Cobalt Nitrate: Co(NO3)2; an extremely useful indicator when working with light-colored infusible minerals; it is used to distinguish calcite from aragonite and is a valuable color indicator of various metals; after wetting the sample with cobalt nitrate solution and intensely heating it, the following colors may be imparted:

  • blue: aluminum minerals, zinc silicates
  • bluish-green: tin oxide
  • yellowish-green: zinc and titanium oxides
  • dark green: antimony and cobalt oxides
  • pink: magnesium minerals

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