Hematite, iron oxide, the chief ore of iron, is found in many places in
Texas but not in large deposits. This mineral may have a metallic luster
and appear reddish brown, dark brown, steel gray, or black or it may
occur as a soft, red, earth-like material called _red ocher_.
[Illustration: Specular hematite from Carrizo Mountains, Hudspeth
County, Texas.]
Most metallic hematite is too hard for a pocket knife to scratch, but
quartz or a steel file will scratch it. Hematite is fairly heavy, for it
has a specific gravity of 5.26. This mineral has no cleavage, but some
specimens show three directions of parting that are almost at right
angles to each other. A great help in identifying hematite is the dark
reddish-brown streak it leaves when you rub it across a streak plate.
Some hematite occurs as rounded masses that resemble kidneys or bunches
of grapes (then called _kidney ore_); it also is found as flat crystals.
Most of the Texas hematite occurs as granular or compact masses. One of
these massive varieties is composed of shiny scales or plates and is
called _micaceous_ or _specular hematite_. This variety has been found
in Hudspeth County and in northeastern Mason County. Hematite also
commonly occurs as cementing material in many Texas sandstones.
Some hematite is formed by the alteration of magnetite, another iron
mineral. This hematite is known as _martite_, and some of it still has
the crystal shape (an octahedron or a dodecahedron) that belonged to the
magnetite. Most of the hematite found in the Llano uplift area of
central Texas is believed to be altered magnetite. In this central Texas
area, some massive, granular martite has been mined at the Gamble
prospect, a few miles southeast of Fredonia in northeastern Mason
County, where it occurs as layers in Precambrian gneiss.
Small deposits of hematite occur in other parts of Texas, too. Some of
the west Texas localities include Sierra Blanca, the Quitman Mountains,
and the Carrizo Mountains of Hudspeth County and the area around Shafter
in Presidio County.
Hollandite. _See_ Manganese Minerals.
Hyalite. _See_ Opal.
Jasper. _See_ Quartz.
Kaolin. _See_ Clay.