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Can someone identify this type of rock?


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I found this rock on the side of the road one morning on my way to school. Ten years later and I still have it, occasionally looking into that sparkly black surface. my guess is it could be some kind of sandstone. Location is Toronto, Canada. Nothing to say about its weight, just a typically heavy rock. Included mouse for size comparison.2178f4ae1eb148f9d471907c6716d416.jpg480092a4482eb29619af928f01c15574.jpg468ce7cbfff79ab7c452b9e3693aaeb7.png

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1 hour ago, IS_IT_SANDSTONE said:

Interesting. Now do the repeating layers represent seasons or something like the rings of a tree?

They would, if it were sedimentary. Gneiss would not be, but schist might be. Most schists are metamorphosed sedimentary rocks, but can sometimes be metamorphosed igneous rocks. 

When there are seasonal layers in sedimentary rocks, they are called varves.

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28 minutes ago, Stillweaver hillbelli said:

If it is derived from sandstone, the layers signify deposition events(flooding) leading to buildup of sands and silt, nothing to do with regular intervals of time.

 

 

It certainly could be regular intervals of time. In areas with seasonal floods the layers would roughly equate to seasons. Maybe not regular intervals of time but definitely seasonal.

In the southwest the rains (and floods) come in late summer. Layers are laid down (or cut away) more or less seasonally. So while the layers are not one for each year like the rings on a tree they are certainly indicative of seasonal events.

Kinda like rattles on a snake. There may not be one for every year but you can assume those rattles were added (or lost) in the summer months.

:brows:

 

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d-day is correct, this is a schist, a metamorphic rock type. 

The "bands" represent the platy minerals aligning themselves perpendicular to the direction stress.  Schist usually represent sandstones or siltstones (sedimentary rock types) that have experienced high temperature/pressure environments which  changed the clays and silts into "new" minerals, that is they have been metamorphosed; thus the metamorphic rock type. 

A few igneous rocks can also be metamorphosed into schist, as d-day stated.

Edited by 4meter
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