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 |