dolomite - student specimens of Ordovician dolomite - Unit of 10 smaller specimen
This particular metamorphic rock can look like marble or it can look like limestone. In this case it looks like a fine-grained white marble. It differs from marble in having some or all of the calcium in calcium carbonate replaced by magnesium. This replacement can occur with or without metamorphic heating. Before metamorphism it was a limestone. If not heated and recrystallized, it would have looked just like the original limestone though some of the calcium had been replaced by magnesium.
If heated by deep burial or by a nearby intrusive body, limestone will recrystallize as in this specimen, taking on the appearance of marble.
Marble and limestone are calcium carbonate and effervesce freely with dilute hydrochloric acid. Dolomite, calcium-magnesium carbonate, will effervesce weakly and may need to be powdered as when lightly tapped by a geologist's hammer to encourage effervescence.
These specimens were collected from the Upper Ordovician Ely Springs Formation in the Inyo Range in California.
If you are a science or earth science teacher purchasing this as teaching specimens for your class, your students should compare this with marble, with limestone and with dolomite that looks like limestone. It will surprise them that dolomite can look both like crystalline marble and like sedimentary limestone.
Though these are smaller than what we usually offer, they are completely adequate for this rock type, as the texture is the same all the way through. Definitely not the tiny fingernail size that we don't think belongs in a classroom. This is an opportunity to save on a classroom set.
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