THE MINERAL AGARDITE

  • Chemistry: (La, Y, Ca, Ce, Nd)Cu6(AsO4)3(OH)6 - 3H2O, Hydrated Lanthanum Yttrium Calcium Cerium Neodymium Copper Arsenate Hydroxide
  • Class: Phosphate Class
  • Subclass: Arsenates
  • Group: Mixite
  • Uses: A very minor source of rare earth metals and as mineral specimens
  • Specimens

Agardite is a rare earth arsenate mineral with a beautiful crystal habit and color. It is also known by the synonym "chlorotile". Agardite is also known officially by two names called agardite-(Y) and agardite-(La) to denote the increased abundance, in these minerals, of the elements yttrium and lanthanum respectively. Agardite-(Ce) is an unoffical variety with an abundance of cerium as is agardite-(Nd) with an abundance of neodymium. These are unoffical names and probably are insignificant or only locally abundant. All are dealt with together here due to their similarities.

Yttrium, cerium, neodymium and lanthanum belong to a group of elements called rare earth metals. The rare earth metals were given this nickname because they were thought to be extremely rare in the Earth's crust. Now many of them are thought to be as common an element as silver. Despite this, as the label implies, these metals are rare in the Earth's crust or more accurately they are rarely concentrated enough to be mined in large quantities. The reason for this rarity of concentration is that these elements are incorporated into other commoner minerals as mere traces with far too low of concentrations to be used as ores. There just is no good concentrating effect as there exists with other valuable metals, making any mineral that possesses them a rarity.

Agardite can form tufts of fine acicular (hair-like) crystals. These tufts are similar to other minerals such as okenite, millerite and artinite, but with one big difference, the color. Agardite has beautiful color that is typically one of several attractive shades of light green. Malachite can form similar tufts and has a green color as well, but is darker green and reacts to hydrochloric acid. Its color, chemistry and form make agardite a very special mineral.

PHYSICAL CHARACTERISTICS:

  • Color is blue-green to yellow-green.
  • Luster is vitreous to silky.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is hexagonal.
  • Crystal Habits include tufts of acicular crystals.
  • Cleavage not noticeable.
  • Fracture is conchoidal.
  • Hardness is 3 - 4.
  • Specific Gravity is approximately 3.6 - 3.7 (above average for translucent minerals)
  • Streak is green.
  • Associated Minerals are limonite, adamite, mimetite and olivenite.
  • Notable Occurrences include Bou Skour Mine, Jbel Sarhro, Morocco; lavrion, Greece; Clara Mine, Germany; Wheal Alfred Mine, Cornwall, England; Red Cloud Fluorite Mine, Lincoln County, New Mexico and Utah, USA.
  • Best Field Indicators are color, crystal habit, density and associations.
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