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New Mexico Geochronology Research Laboratory
Mineral/rock 40Ar/39Ar dating potential

If you are interested in obtaining 40Ar/39Ar dates, please contact one of the NMGRL staff for costs and turn-around time.

Below are some of the more common rocks and minerals that have been dated by the NMGRL.

Volcanic Minerals

Rock/Mineral
Percent
K2O
Advantages
Disadvantages

Anorthoclase

<3%
high potassium; homogenous
rare excess argon observed (melt inclusions)

Biotite/Phlogopite

~3%
High potassium; Often easy to separate from host rock
Hydrous; May contain excess argon; Commonly variably altered to chlorite

Glass

variable
Common; Easy to prepare from host rock
Alters/hydrates easily; Susceptible to 39ArK recoil
Groundmass
Wholerock
variable
Very common; Easy to prepare/analyze
Inhomogeneous; May contain inherited argon (excess argon or xenocrysts); Commonly variably altered
Hornblende
<1%
Common
Low potassium; Hydrous; May contain excess argon
Plagioclase
<2%
Very common
Low potassium
Pyroxene
<1%
Common
Low potassium; Hydrous; May contain excess argon
Sanidine
>3%
High potassium; Very homogenous; Easy to separate/analyze
- -

Plutonic Minerals

Rock/Mineral
Percent
K2O
Advantages
Disadvantages
Biotite/Muscovite
>3%
High potassium; Common; Often easy to separate from host rock
Hydrous; May contain small quantities of excess argon
Hornblende
<1%
Common; Often easy to separate from host rock
Low potassium; Hydrous; May contain small quantities of excess argon
Potassium Feldspar
>5%
High potassium; Common; Easy to separate from host rock
Rare excess argon observed (fluid inclusions)

Metamorphic Minerals

Rock/Mineral
Percent
K2O
Advantages
Disadvantages
Biotite/Muscovite
>3%
High potassium; Common; Often easy to separate
Hydrous; May contain excess argon
Hornblende
<1%
Common; Often easy to separate
Low potassium; Hydrous; May contain excess argon

Hydrothermal Minerals

Rock/Mineral
Percent
K2O
Advantages
Disadvantages
Alunite
variable
Capable of dating low temperature
mineral deposition
Hydrous; susceptible to 39ArK recoil and reactor induced 40Ar loss
Jarosite
variable
Capable of dating low temperature
mineral deposition
Hydrous; susceptible to 39ArK recoil and reactor induced 40Ar loss

Sedimentary Minerals

Rock/Mineral
Percent
K2O
Advantages
Disadvantages
Glauconite
~3-5%
Capable of dating sedimentary deposition
Susceptible to 39ArK recoil and reactor induced 40Ar loss