Poikilo-ophitic dolerite
A rock subtype
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Poikilo-ophitic dolerite refers to a specific type of dolerite (also known as diabase or microgabbro) characterized by its distinctive poikilo-ophitic texture observed under a microscope.
Texture Description
The texture is a variety of the more general poikilitic texture, in which:
Plagioclase feldspar crystals (specifically laths, or elongated crystals) are completely or partially enclosed within much larger, anhedral (irregularly shaped) crystals of pyroxene (commonly augite) or sometimes other minerals like olivine or hornblende.
The enclosed plagioclase crystals are referred to as chadacrysts, and the large enveloping pyroxene crystal is called an oikocryst.
This arrangement gives the rock a characteristic mottled or speckled appearance, especially in hand specimens or under a microscope, where numerous small plagioclase laths are 'floating' inside the larger pyroxene grains.
Formation and Occurrence
This texture is characteristic of many dolerites and gabbros and is related to the specific cooling history of the magma. It is thought to develop when the plagioclase nucleates and grows faster than the pyroxene, which then crystallizes later, enveloping the pre-existing feldspar laths.
Texture Description
The texture is a variety of the more general poikilitic texture, in which:
Plagioclase feldspar crystals (specifically laths, or elongated crystals) are completely or partially enclosed within much larger, anhedral (irregularly shaped) crystals of pyroxene (commonly augite) or sometimes other minerals like olivine or hornblende.
The enclosed plagioclase crystals are referred to as chadacrysts, and the large enveloping pyroxene crystal is called an oikocryst.
This arrangement gives the rock a characteristic mottled or speckled appearance, especially in hand specimens or under a microscope, where numerous small plagioclase laths are 'floating' inside the larger pyroxene grains.
Formation and Occurrence
This texture is characteristic of many dolerites and gabbros and is related to the specific cooling history of the magma. It is thought to develop when the plagioclase nucleates and grows faster than the pyroxene, which then crystallizes later, enveloping the pre-existing feldspar laths.
Unique Identifiers
Mindat ID:
498929
Long-form identifier:
mindat:1:1:498929:1
Classification of Poikilo-ophitic dolerite
Mineralogy of Poikilo-ophitic dolerite
Essential minerals - these are minerals that are required within the classification of this rock:
| Feldspar > Plagioclase | (Na,Ca)[(Si,Al)AlSi2]O8 |
| Pyroxene | ADSi2O6 |
Internet Links for Poikilo-ophitic dolerite
mindat.org URL:
https://www.mindat.org/min-498929.html
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References for Poikilo-ophitic dolerite
Reference List:
Localities for Poikilo-ophitic dolerite
symbol to view information about a locality.
The Locality List
- This locality has map coordinates listed.
- This locality has estimated coordinates.
ⓘ - Click for references and further information on this occurrence.
? - Indicates mineral may be doubtful at this locality.
- Good crystals or important locality for species.
- World class for species or very significant.
(TL) - Type Locality for a valid mineral species.
(FRL) - First Recorded Locality for everything else (eg varieties).
All localities listed without proper references should be considered as questionable.
Russia | |
| Голубев et al. (2008) |