FMF - Friends of Minerals Forum, discussion and message board

[Josele]

Often the word matrix is used in mineral forums as the substrate of the main specie or most prominent crystals of a specimen, even when this substrate is another mineral specie and not the rock where these minerals have developed.
Would't be better to keep the concept of matrix as synonym of mother rock only?

[Bob Harman]

I fully agree with Josele's concept of the word "matrix". Here in the sedimentary environment of Indiana, the matrix is almost always limestone or closely related dolostone.

When I discuss the whole specimen, I would include the limestone (or dolostone) matrix as as a part of the whole specimen, but if discussing the collector part of the specimen, I leave out the matrix, just noting the mineral(s) upon the other mineral as its bed.

Here are 2 examples of very many from my collection. BOB

[Kevin Schofield]

[Jesse Fisher]

I am not sure that the terms "matrix" and "mother rock" are synonymous, as "mother rock" implies a genetic relationship and "matrix" does not. In the case of crystals developing in an igneous or metamorphic environment, there is not an outside infiltration of mineralizing solutions that are responsible for crystal growth. This is not the case in deposits of hydrothermal or metasomatic origin, where the "host rock" is pre-existing and the crystals of interest were the result of invading mineralizing solutions. The host rock is often highly altered during the mineralizing process, which may influence the chemistry of the environment in which the crystals grow, but it is not necessarily responsible for providing the basic ingredients for the crystallizing minerals.

A good example is the specimen below, a fluorite with calcite from the Heights Quarry, Weardale, England. The host rock for these mineral deposits is limestone of Carboniferous age, which was tectonically fractured and then invaded by mineralizing fluids of Permain age. The host limestone has been altered to varying degrees by this process, and in this case, the calcium carbonate that formed into crystals of calcite was likely derived from it. The fluorine necessary for the fluorite was likely derived from a deep-seated igneous source and introduced to the limestone through the circulation of heated groundwater. Sulfides such as galena and sphalerite are also common in these mineral deposits, and is thought to have formed in a similar fashion. I think that referring to the altered limestone on which the fluorite crystals sit as "mother rock" would be incorrect.

[Bob Carnein]

I agree with Jesse Fisher. To me, the term "host rock" is more useful. Geologists generally use the term "matrix" for material surrounding and enclosing some interesting feature, such as a fossil. But, like many terms, there are inconsistencies in its use.

[Josele]

Let me clarify that I used the concept "mother rock" as literal translation of roca madre which is Spanish is synonym of "host rock" (roca encajante) and also synonym of "matrix rock" (roca matriz). I don't know if in English these concepts are synonyms too.

In short I would describe Jesse specimen as "fluorite and calcite on limestone matrix" but is really better Jesse description with the explanation of his genesis.

[Matt_Zukowski]

I believe you are right that this is a language thing. I have never heard the term "mother rock" except in talking to non-english speaking mineral enthusiasts. The term "host rock" brings to my mind a mineral deposit context. In my english context, "matrix" is the term for what we are referring to when describing something on something else. Even for syngentic material like "garnet on a schist matrix."

[Vinoterapia]

There is probably more than a simple question of language, but in which industry context the term is used. The Spanish term "roca madre" is widely used in the oil industry as the equivalent of the English term "source rock" ( ie. where the hydrocarbons were formed), probably in that industry nobody would use it as a synonym of "host rock".

[Roger Warin]

Hi,
About the crystal support matrix.
This topic is somewhat off-topic. However, the notion of support (the matrix) comes into play.
In a glass bottle, the stopper is the only support for the occurrence of crystalline organic germs.
When the young wine is aged in the cellar, the lees are deposited and at the same time, tartar crystals appear only on contact with the cork, which by its roughness and its cellulosic nature is a favorable ground for inducing the appearance of crystalline germs from various organic salts including acidic K tartrates or sodium-potassium tartrate. Already in the old processes, chemical manipulations intervened to clarify and stabilize the wines.
These tartrates have a very weak crystalline symmetry, either triclinic or monoclinic.