Menilite is a greyish-brown form of the
mineraloid
A mineraloid is a naturally occurring substance that resembles a mineral, but does not demonstrate the crystallinity of a mineral. Mineraloid substances possess chemical compositions that vary beyond the generally accepted ranges for specific mi ...
opal
Opal is a hydrated amorphous form of silicon dioxide, silica (SiO2·''n''H2O); its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Due to the amorphous (chemical) physical structure, it is classified as a ...
.
[Menilite on Mindat.org]
/ref> It is also known as ''liver opal'' or ''leberopal'' (German), due to its color. It is called menilite because it was first described from Ménilmontant
Ménilmontant () is a neighbourhood of Paris, situated in the city's 20th arrondissement. It is roughly defined as the area north of the Père Lachaise Cemetery, south of Parc de Belleville, and between ''Avenue Jean-Aicard'' on the west an ...
(Paris
Paris () is the Capital city, capital and List of communes in France with over 20,000 inhabitants, largest city of France. With an estimated population of 2,048,472 residents in January 2025 in an area of more than , Paris is the List of ci ...
), France
France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
,[ where it occurs as ]concretion
A concretion is a hard and compact mass formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular shapes a ...
s within bituminous
Bitumen ( , ) is an immensely viscous constituent of petroleum. Depending on its exact composition, it can be a sticky, black liquid or an apparently solid mass that behaves as a liquid over very large time scales. In American English, the m ...
Early Oligocene
The Rupelian is, in the geologic timescale, the older of two age (geology), ages or the lower of two stage (stratigraphy), stages of the Oligocene epoch (geology), Epoch/series (stratigraphy), Series. It spans the time between . It is preceded b ...
Menilite Shale
Menilite is a greyish-brown form of the mineraloid opal. It is also known as ''liver opal'' or ''leberopal'' (German), due to its color. It is called menilite because it was first described from Ménilmontant (Paris), France, where it occurs as ...
s.
See also
* Geyserite
Geyserite, or siliceous sinter, is a form of opaline silica that is often found as crusts or layers around hot springs and geysers. Botryoidal geyserite is known as fiorite. Geyserite is porous due to the silica enclosing many small cavities. Si ...
* Hyalite
Hyalite is a transparent form of opal with a glassy lustre. It may exhibit an internal play of colors if natural inclusions are present. It is also called Muller's glass, water opal, and jalite. Müller's glass is named after its discoverer, ...
References
Opals
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