Minerals

Slickensides

Calcite slickensides form in cracks (faults) in rock/sediments.
Loc: Dallas Co., TX.	Loc: Dallas Co., TX.	Loc: Dallas Co., TX.

Gypsum

Gypsum Loc: Knox Co., TX.	Gypsum Loc: Knox Co., TX.	Gypsum Loc: Knox Co., TX.
Gypsum Loc: Knox Co., TX.	Gypsum Loc: Knox Co., TX.	Gypsum Loc: Knox Co., TX.
Loc: Tarrant Co., TX

Phosphatic (septarian) nodules (with crystals inside)

"septarian" nodule Loc: Dallas Co., TX.	Calcite crystals inside nodule. Loc: Dallas Co., TX.
"septarian" nodule Loc: Dallas Co., TX.	"septarian" nodule Loc: Dallas Co., TX.	"septarian" calcite crystals Loc: Dallas Co., TX.
"septarian" calcite crystals Loc: Dallas Co., TX.	"septarian" calcite crystals Loc: Dallas Co., TX.	"septarian" calcite crystals Loc: Dallas Co., TX.

Pyrite and marcasite

Marcasite is a less stable form [different crystallization] of pyrite and should not be kept with true pyrite.  Marcasite releases sulfur which produces sulfuric acid.  Pyrite's chemical formula is FeS2 (aka Iron Sulfide).
Pyrite Loc: Ellis Co., TX.	Marcasite? Loc: Dallas Co., TX.	Rare wild cubed pyrite Loc: Denton Co., TX.

Other

black nodule Loc: Dallas Co., TX.	Hematite?? Loc: Jack Co., TX.
An amazing preservation of ammonite chambers. Possibly from stacked Placenticeras ammonites. Loc: Dallas Co., TX. 2019 [no specific date]
Septarian nodule with ammonite inside. Loc: Dallas Co., TX. 2006?
29 April 2017

Rocks (mineral composites)

Here are some miscellaneous rocks that are in my collection either purchased or picked up wherever.
Potassium Feldspar (pink mineral)	Potassium Feldspar (pink mineral)
Wikipedia "Rhyolite is an extrusive igneous rock, formed from magma rich in silica that is extruded from a volcanic vent to cool quickly on the surface rather than slowly in the subsurface. It is generally light in color due to its low content of mafic minerals, and it is typically very fine-grained (aphanitic) or glassy."
Rhyolite washed into a creek (imported).	Rhyolite washed into a creek (imported).
Rhyolite washed into a creek (imported).	Rhyolite washed into a creek (imported).
Comparison with the "Thunderbird" Rhyolite of West Texas.