Vogesite
Lamprophyre; hornblende + augite with alkali feldspar (orthoclase) groundmass
A dark hornblende-rich lamprophyre dike rock with amphibole and augite phenocrysts in an alkali-feldspar-dominated groundmass.
- Mohs hardness
- 5-6
- Color
- dark gray to greenish black
- Type
- igneous
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Overview
Vogesite is a calc-alkaline lamprophyre defined by phenocrysts of hornblende (amphibole), often with augite, set in a groundmass in which alkali feldspar (orthoclase) dominates over plagioclase. It is the hornblende-bearing, alkali-feldspar counterpart within the lamprophyre family.
Like other lamprophyres it forms dark, porphyritic, mafic dikes and small intrusions rather than large plutons. It is named after the Vosges Mountains of eastern France, where it was first described.
Vogesite is essentially a petrological category — a dark dike rock of academic interest rather than a commercial material.
Formation & geology
Vogesite crystallizes from hydrous, mafic magma emplaced as thin dikes and sills in the shallow crust. The abundant water in the melt promotes growth of hydrous hornblende phenocrysts, while the residual liquid solidifies into an alkali-feldspar-rich groundmass.
It is typically associated with late- to post-orogenic magmatism, often intruding along fault zones in mountain belts after the main granitic plutonism. Occurrences cluster in Hercynian and Caledonian terranes, including the Vosges type area and similar provinces across Europe and North America.
How to identify it
Look for a dark, porphyritic dike rock with elongate, glassy-black hornblende crystals and possibly stubby augite set in a finer dark matrix. Hardness is moderate (about 5-6).
The defining contrast within lamprophyres is mineralogical: vogesite has hornblende as the main dark mineral and alkali feldspar in the groundmass. Spessartite is its plagioclase-dominant hornblende counterpart, while minette and kersantite are the mica lamprophyres.
Look-alikes include diorite porphyry and other lamprophyres. Distinguishing vogesite from spessartite, in particular, requires identifying the dominant feldspar, which generally means thin-section examination.
Uses & significance
Vogesite has no significant commercial use. Like other lamprophyres it may locally serve as crushed rock, but its dike-scale occurrence makes it unimportant as a resource.
Its value is scientific and educational: it is a named reference rock used in teaching lamprophyre classification and in studies of mantle-derived, hydrous magmatism in orogenic belts. Collectors of named igneous types seek type-area specimens.
It has no jewelry or metaphysical tradition.
Frequently asked questions
What distinguishes vogesite from other lamprophyres?
It has hornblende as the dominant dark mineral and alkali feldspar (orthoclase) dominating the groundmass.
How is vogesite different from spessartite?
Both are hornblende lamprophyres, but vogesite's groundmass is dominated by alkali feldspar while spessartite's is dominated by plagioclase.
Where does the name vogesite come from?
From the Vosges Mountains in eastern France, the type locality.
Does vogesite form large intrusions?
No. Like other lamprophyres it occurs mainly as dikes, sills, and small bodies.
Vogesite guides
In-depth guides for identifying, valuing, and understanding Vogesite.
