Petrified Wood or Rock?

[Cachersusie]

I found a few pieces of this in a creek in an area where the water flows pretty good.  Can anyone tell if it is petrified wood or just rock? Found in Post Oak Creek, Grayson County, Texas. Thank you in advance.

[Cachersusie]

Here is the other side.

[ynot]

Could be selenite. (satin spar) 

[DPS Ammonite]

Interesting rock. It is a piece of slickenside calcite that forms in joints and faults in the area. It records the effects of rocks grinding against each other. I once was fooled into thinking that these were petrified wood. After seeing some pieces in the faults, I figured out what they were. I have some slickensides that have a nearly mirror finish.

[Cachersusie]

They are rather pretty! Thank you for taking the time to tell me about them.

[Fossildude19]

More information on Slickensides.

[FossilsAnonymous]

It sure is interesting, but I agree with the others, some sort of Slickenslide. I think it's cool though.

[Cachersusie]

Thank you all for helping!

 

[Tidgy's Dad]

I think selenite. 

[abyssunder]

I would go with "Satin Spar' on this. Try to determine its hardness in the Mohs scale.

[DPS Ammonite]

38 minutes ago, abyssunder said:

I would go with "Satin Spar' on this. Try to determine its hardness in the Mohs scale.

We need to get a hardness to show that it is most likely calcite. I have personally seen and collected many of the slickensided calcite pieces. What I found unusual about them is that they have many planes of slip inside of them instead of having just a plane exposed on the outside. I suspect that some of the calcite actual grows in an elongated fibrous form. Most of this calcite probably comes from dissolved limestone that is common in the area. I have yet to see any large pieces of gypsum in the area.

 

 

[JohnJ]

1 minute ago, DPS Ammonite said:

We need to get a hardness to show that it is most likely calcite. I have personally seen and collected many of the slickensided calcite pieces. What I found unusual about them is that they have many planes of slip inside of them instead of having just a plane exposed on the outside. I suspect that some of the calcite actual grows in an elongated fibrous form. Most of this calcite probably comes from dissolved limestone that is common in the area. I have yet to see any large pieces of gypsum in the area.

 

 

 

 

'DPS' John is right; this is a piece of calcite that is very common to Grayson County and other areas of North and Central Texas.

 

[Cachersusie]

These look exactly like what I have and other pieces we saw in the creek.  

[abyssunder]

As I expected, someone would know that.
I asked for the hardness to make the difference between "Calcite Satin Spar", and "Gypsum Satin Spar". link

[ynot]

Regardless of what the mineral is, there is no slickensides here. 

Slickensides is the markings left when 2 rocks are abrated while moving past each other. This material is a crack filling (vein).

The "streaked" appearance is from the nature of the mineral, and how it brakes on cleavage planes.

[Cachersusie]

I'll check for the hardness when I get back home tomorrow.  How do I go about doing that? You all have been so helpful. 

[ynot]

6 minutes ago, Cachersusie said:

I'll check for the hardness when I get back home tomorrow.  How do I go about doing that? You all have been so helpful. 

Take a small piece off and see if it will scratch a copper penny or a knife blade.

[DPS Ammonite]

3 hours ago, ynot said:

Regardless of what the mineral is, there is no slickensides here. 

Slickensides is the markings left when 2 rocks are abrated while moving past each other. This material is a crack filling (vein).

The "streaked" appearance is from the nature of the mineral, and how it brakes on cleavage planes.

The slickensides from the limestone areas of North Texas are weird creatures. Some of them have highly polished recent movement marks. Some look quite old. I have seen them in faults with offsets and in cracks and joints with very little offset. Because the faults, cracks and joints are conduits for water, I suspect that parts of them might be dissolved and redeposited. Some of them might be sort of molds and casts of slickensides or partially dissolved slickensides.

 

Someone suggested that slickensides might be formed in joints and cracks that move up and down quakes but do not end up with an offset when the quake stops, sort of vibrational polishing. I have yet to find a reference that proves that method of formation. It sort of makes sense that large blocks of limestone separated by cracks and joints would move up and down relative to each other during a quake. I saw a recent video of an earthquake at Kilauea summit that showed cracks in a concrete slab and rock open and close and go up and down. There must be some sort of rub marks in the wall and in the concrete.

 

Here is a prior post with two North Texas slickensides that I found. The first one shows high polish marks.: 

 

 

 

[Cachersusie]

Well I broke it open with a hammer and I don't know if I did it correctly but it did scratch the penny. The inside is very pretty.

[Cachersusie]