MINERAL PROPERTIES and identification procedures
EFFLORESCENCE, DELIQUESCE,
TRANSFORMATION, and DECOMPOSITION
A number of detrimental properties in certain minerals cause them to undergo
chemical changes in particular circumstances. Special conditions must be provided to
preserve these minerals. (See "Storing Minerals"
for information on protecting specimens from these conditions.)
Efflorescence
Efflorescence is the loss of water from the chemical structure of a mineral. A small
number of hydrous minerals may partially
lose the water in their structure if
kept in dry or hot areas. This causes the mineral to form a white powder on its surface,
and decreases its transparency. Some minerals eventually crumble from efflorescence.
Deliquesce
Deliquesce is the opposite of efflorescence –
it is the absorption of water into the chemical
structure of a mineral. This property is only present in a few water-soluble minerals.
Atmospheric water (humidity) gets absorbed into the structure of a mineral, thereby
destroying its crystal lattice and
causing it to dissolve. The most common delinquent minerals are sylvite, carnallite, and
some specimens of halite.
Transformation
Some minerals transform into other minerals under
stress, heat, and prolonged exposure to light. Some minerals, upon loss of water transform
into other minerals. Three examples are:
- Borax:
Na2B4O7 · 10H2O
transforms into tincalconite
– Na2B4O7 · 5H2O
- Torbernite: Cu(UO2) 2
(PO4) 2 · 8-12H2O
transforms into meta-torbernite – Cu(UO2) 2
(PO4) 2
- Autunite: Ca(UO2) 2
(PO4) 2 · 8-12H2O
transforms into meta-autunite Ca(UO2) 2 (PO4)
2
A common and well-known transformation is realgar to
orpiment. Bright red realgar specimens (AsS) transform into golden-yellow orpiment (As2S3) when exposed to
prolonged light.
Decomposition
A small number of minerals decompose in certain
circumstances. Orpiment crumbles into a yellow powder when exposed to prolonged light. Marcasite occasionally develops a
whitish encrustation "growth" on its surface that eventually causes it to
disintegrate. This growth may spread to other sulfide minerals in a collection and cause
them to disintegrate as well. This condition is not fully understood, and it only strikes
certain marcasite specimens at random. This condition, known as "pyrite decay",
is usually unpredictable.
Color Change
Some minerals undergo color changes in different
lighting conditions or when exposed to radiation. For more information on this, see Color in mineral properties.
Copyright ©
1997 - 1999 Hershel Friedman, all rights reserved
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