Re-discovering Lampasas Celestite

This 10-inch celestite cluster was recently collected
in Central Texas by Shawn Maddox of Austin. Shawn
also collected and displayed the calcite below at the
Austin Gem and Mineral Show Nov. 12-14, 1999.

By Joe Lobell

(The following article was published in Rocks and Minerals, March-April, 1992. I prefer the name "celestite" to the officially-approved "celestine," so strontium sulfate will be referred to as "celestite" throughout this website.)

Click on the camera for specimen photos

 

The region surrounding the city of Lampasas, Texas (and the county of the same name) has long been recognized as a source area for celestite crystals. But finding representative specimens on the mineral market, at least during the past few years, has been difficult.

Several factors have probably played roles in the relative scarcity of Lampasas celestite specimen material. For example, the author knows of no major ongoing quarries or mining operations in the celestite-producing zones near Lampasas. Collecting from outcrops has been erratic, and most of the land is under private (often absentee) ownership, so access to producing sites is occasionally difficult or impossible. Also, interest in collecting Lampasas-area celestite has likely been tempered by the relative abundance and unique coloration of celestite from around Austin, 70 miles (ll0 kilometers) southeast of Lampasas. Frequent construction projects and quarries in the Austin area have provided good sources for distinctive, unweathered pale blue or blue-tipped celestite crystals.

Geographically, Lampasas is located in that part of central Texas commonly known as the "Hill Country," a sprawling region extending generally 150 to 300 kilometers west of a line from Waco to San Antonio. Considered in this article are Lampasas County and portions of the nearby counties of Brown, Mills, Hamilton, Coryell, Bell, Burnet and Williamson.

The region's landscape is a mosaic of clear, spring-fed creeks, rolling pastureland, and long, grassy or wooded ridges, occasionally bounded by steep limestone bluffs. Ranching of cattle, sheep and goats is the major economic activity in the rural areas. Lampasas, Gatesville, Burnet, Goldthwaite and Copperas Cove are the major communities within the region.

Most Lampasas-area residents who have celestite on their properties are unaware of its existence. Many of those who are aware refer to it (or calcite, a frequent associate) as "glass rock" or "quartz."

The objective of this report is to document occurrences of celestite and associated minerals within the designated area.

HISTORY

Many mineralogy texts and field guides list Lampasas as a celestite locality.

Apparently, Lampasas first became "famous" for its celestite more than a century ago, about the time railroads were being constructed through the area. Kunz (1886) cites a celestite occurrence of a crystal measuring 20x13x10 centimeters in a railroad cut near Lampasas. The crystal is described as "of a fine skyblue color." Cummins (1889) describes perhaps the same occurrence (although identifying the mineralization as strontianite) near the head of Little Lucy Creek, about six miles (10 kilometers) north of Lampasas, and mentions a second location northwest of Lampasas near the head of Lynch Creek in the vicinity of the Nix community.

One such specimen obtained during this early period is mentioned in an advertisement by Lawrence Conklin in the Jan.-Feb. 1990 issue of The Mineralogical Record, which documents a letter from Dr. A.E. Foote to renowned collector C.S. Bement. Foote states in the April 21, 1886, letter that he had purchased an outstanding blue celestite specimen found near Lampasas for $35. According to Foote, the specimen came from a railroad cut which he visited and came away from without "a single particle of blue celestite." The specimen obtained by Foote was purchased by Bement for $50. The specimen is now in the American Museum of Natural History.

Taff (1891) specifies celestite as occurring on Donalson Creek east of Nix, and along Rocky, North Rocky and South Rocky creeks in Burnet County. Chamberlain (1895) mentions celestite crystals in a now-uncertain location along "Limekiln Creek" in Burnet County.

Hill (1901) documents the now-famous Mt. Bonnell and Mt. Barker locations in Travis County near Austin, and goes on to mention celestite occurrences in Lampasas and Burnet counties (citing earlier references), and adds Bell, Williamson and Coryell counties to the celestitie-producing list. He also states (and this author believes very accurately) that the celestite pockets "apparently occupy a persistent horizon in the Glen Rose formation."

Additional documentation of Lampasas-area celestite occurrences is provided by Simonds (1902), citing an earlier reference by Dana to crystals "sometimes of gigantic size" five miles (eight kilometers) north of Lampasas. Simonds also mentions the occurrence of celestite crystals near Strickling in Burnet County.

L. Brown (1930) refers to two celestitie-bearing zones with distinct crystal types within the Glen Rose formation. Evans (1943) focuses on commercial celestite deposits in the Nolan, Sweetwater and Blanket districts.He does mention celestite occurrences at Little Lucy Creek six miles (10 kilometers) north of Lampasas, in Mills County four miles (six kilometers) east of Zephyr, and in Williamson County along the San Gabriel River north of Leander.

Mills County locations are mentioned by Stenzel et. al. (1948) and Havins (1948). Dreyer (1968, 1970, 1971) notes the occurrence of celestite crystals at several locations, including Cowhouse Creek in Coryell County. A. Brown (1974), in his study on the origin and occurrence of central Texas celestite, provides five additional locations in Lampasas County and one each in Mills, Bosque and Hamilton counties.

Smith (1990) compiles many of these locations and several more recent finds in his "Texas Mineral Locality Index."

It seems probable from historical evidence that the original "Lampasas" celestite collecting localities were associated with Little Lucy Creek and/or a railroad cut nearby. These locations apparently produced a very small quantity of excellent celestite more than 100 years ago, and very little specimen material since.

RECENT ACTIVITIES

Mineral collectors, rockhounds, researchers, mineral club groups and university students have collected celestite intermittently in and around Lampasas for many years, but only a few have documented their finds.

During the summer of 1989, the author, along with several friends, began a systematic survey of celestite in Lampasas and surrounding counties. Since that time, more than sixty additional occurrences of celestite have been found, and the search is by no means comprehensive or complete.

GEOLOGIC SETTING

The celestite of the Lampasas area occurs within the Glen Rose Formation of Lower Cretaceous age. The Glen Rose Formation consists of a series of horizontally-bedded limestones, dolomites and marls that were deposited in environments that varied between marine back-reef lagoonal and sabhka shoreline. This is attested to by the numerous marine invertebrate fossils and dinosaur tracks in some areas.

The Glen Rose in the area of Lampasas County is essentially flat and thickens toward the east. Major faulting is generally absent. A detailed description of the Glen Rose stratigraphy and an extensive list of references is provided by Pitman (1989). Exposures of the Glen Rose occur in stream beds and bluffs. The uneven weathering of resistant and recessive zones in the formation results in a characteristic "stair-step" topography.

The celestite forms in solution cavities that range from a couple of centimeters to more than half a meter in diameter. These cavities occur in zones that can sometimes be correlated over large distances. Brown (1974) suggests that virtually all the celestite is secondary in origin and forms in solution cavities that were originally occupied by anhydrite. Several beds of anhydrite or gypsum occur in the Glen Rose or equivalent formations of central Texas, east Texas and southwest Arkansas. Recent work by Slaughter et. al. (1987) in southwest Arkansas indicates that the anhydrite or other evaporites are probably the source of the strontium.

Each celestite zone is often distinctive in terms of crystal size, habit and associated minerals. As many as five celestite zones can be found in the eastern part of the study area where the Glen Rose is thicker.

 

MINERALS

Celestite and calcite are the most abundant minerals occurring in the solution cavities. Minor amounts of pyrite and/or marcasite occur as inclusions in celestite and calcite and coatings on celestite. A white to yellowish alteration product encrusting celestite and calcite is generally strontianite.

A. Brown (1974) also reports finding microscopic inclusions of anhydrite within celestite, supporting his contention that all the Lampasas-area celestite is secondary. Celestite casts preserved by calcite or limestone encrustations occur at several locations.

An accompanying map indicates the geographic distribution of known celestite occurrences in Lampasas and nearby counties. A suggested mineral paragenesis of the cavities in the Rodessa member of the Glen Rose is g1ven in an accompanying chart.

Celestite in the Glen Rose formation occurs in a variety of habits, including bladed crystals elongated on the b-axis, prismatic crystals elongated on the a-axis, tabular crystals flattened on the c axis with roughly equal development along a and b axes, bedded layers, and anhedral nodules.

Crystals elongated along the b-axis frequently occur in an uppermost celestite zone at outcrops where more than one zone is present. Along North Sims Creek and several tributaries in northwest Lampasas County and the adjacent area of southeast Mills County, these bladed crystals occur in two persistent and distinctive zones about eight to ten meters apart. In the uppermost zone, the crystals are often "nested" and intergrown. Some of the crystals within the host cavities exhibit a salmon color near their points of contact with the cavity wall. Calcite is conspicuously absent in this uppermost bed.

The lower bed in the North Sims Creek area consists of thick bladed crystals, often with curving or complex multiple terminations. These crystals are flattened on c{001} and elongated along the b-axis. Calcite, as scalenohedral crystals from several millimeters to several centimeters in length (occasionally double-terminated), is a persistent associate. The largest celestite crystals obtained from the lower bed reach a length of more than 25 centimeters. Cavities reach a maximum of more than half a meter in diameter and are often filled with thick, intergrown crystals.

Elsewhere in Lampasas County, the b-axis crystals appear concentrated in a single, persistent, high bed, frequently associated with large (up to 15-centimeter) calcite crystals. At several outcrops the celestite exhibits a narrow white phantom paralleling the m{210} faces. At other outcrops this same bed (or an equivalent) contains calcite only.

Bladed crystals are usually transparent to milky-white on outcrop exposures. Occasionally the tip of a bladed crystal will exhibit a slight blue or blue-gray tinge.

Prismatic crystals elongated on the a-axis usually occur in one or more beds as much as 10 to 15 meters below the b-axis zone(s). These crystals reach 20 centimeters in length and may weigh several kilograms.

In the vicinity of Adamsville (approximately 23 kilometers north of Lampasas) prismatic celestite occurs in the beds, banks and bluffs of several tributary streams to the Lampasas River and Sims Creek. The crystals are milky white, translucent and are sometimes coated with calcite crystals. Many of the crystals are stained brown and yellow from decomposing iron sulfides, especially on the o{011} faces, which tend to be deeply etched or pitted. These crystals only very rarely exhibit clinodome {h,k,l} faces, the commoner forms consisting only of prismsd {101},o{011} and m{210} and pinacoids c{001}. None of the crystals examined contained any a{100) or b(010} forms.

Tabular crystals occur throughout the region and reach perhaps their best development in several beds along Rocky Creek, its tributaries and those of the Lampasas River in Burnet County near Oakalla. The largest unterminated crystals found thus far are 30 centimeters long. The largest well-terminated crystal is 22 centimeters from base to termination.

These tabular crystals exhibit a wide range of tints, including yellowish-brown, clear, gray, pale blue, and very light bluish-green. Some crystals are opaque due to inclusions of capillary or dendritic iron sulfide, often in "streaks" or acicular aggregates near the c{001} surfaces. Calcite is a common associate in some of the Bumet County celestite beds but is absent in others.

Much of the celestite in the region is massive or nodular, either partially or completely filling the cavities. The nodular celestite shows the same color variations as the other habits.

It is interesting to note that celestite from several Lampasas-area deposits tends to become more bluish when protected from strong light for prolonged periods. Crystals found on the surface seldom display any blue coloration, lending support to the theory that sunlight results in a fading of the color. The specific cause of the blue color in Texas celestite is uncertain, but may be due to trace amounts of ytterbium, as reported by Smith (1989).

Bedded celestite is common in Brown County. These beds of pink to white granular celestite are sometimes associated with bluish fibrous celestite up to 25 centimeters thick. The beds occasionally contain cavities, into which project transparent to translucent b-axis bladed crystals up to several centimeters in length. These occurrences appear to correspond to the upper zones of bladed crystals in Mills and Lampasas counties.

FUTURE PROSPECTS

Almost all the celestite collected by the author since May, 1989, has come from streambed, streambank, bluff or hillside exposures and had therefore been exposed to at least some negative effects of weathering. Those few specimens that originated in a more "protected" environment exhibit smooth faces and high luster, and, although lacking the intense blue color of the Austin material, compare favorably with specimens from elsewhere in Texas, Ohio, the Malagasy Republic and other better-known localities.

As stated earlier, virtually all of the collecting sites are located on private land. Ranchers zealously guard their property rights, especially in the winter months during deer season. Rattlesnakes, copperheads, scorpions and abundant ticks present persistent concerns the remainder of the year.

Nevertheless, the prospect of obtaining exceptional celestite specimens in the area is possible if not probable, especially if excavation or other efforts produce "fresh," unweathered material. The deposits appear to be persistent and widespread, and a new discovery is possible anywhere the appropriate Glen Rose bed is exposed.

ACKNOWLEDGMENTS

The author would like to express sincere appreciation to David Patzke, whose friendship has proven both enjoyable and practical on numerous collecting and exploring trips; Frank and Marilyn Morris, enthusiastic collecting companions who also provided valuable geological and grammatical insight; John Kincel and Paul Concilio, who accompanied the author on several weekend expeditions; and Arthur Smith and Al Kidwell, whose advice, geological expertise, manuscript review and encouragement have proven invaluable.

And special thanks are also due the many friendly property owners who, by allowing access to their land, brought us many hours of collecting and exploring pleasure and contributed to the ever-expanding realm of mineralogical knowledge.

REFERENCES

  • Brown, A. 1974. Occurrence and Origin of Celestite, Glen Rose Formation, Central Texas. Unpublished student paper, Baylor University, Waco, Texas.
  • Brown, L.S. 1930. Types, Occurrence and Probable Origin of Texas Celestite. In American Mineralogist 15:121-122.
  • Chamberlain, A. 1895. In The Mineral Collector, vol. 2, no. 5, p. 81.
  • Conklin, L.H. 1990. In The Mineralogical Record, vol. 21, p. 105.
  • Cummins, W.F. 1889. The Southern Border of the Central Coal Field. Texas Geological Survey, First Annual Report, p. 162.
  • Dreyer, B.V. 1968. The Glen Rose Limestone in Coryell County. Unpublished student paper, Baylor University, Waco, Texas.
    • ---1970. A Petrologic Study of the Glen Rose Limestone in Coryell and Lampasas Counties. Unpublished student paper, Baylor University, Waco, Texas.
    • ---1971. Stratigraphy of the Trinity Group (Northeast side of the Llano Uplift), Central Texas. Unpublished master's thesis, Baylor University, Waco, Texas.
  • Evans, G.L. 1943. Celestite Deposits in Texas. Univ. Texas Publication 4301: 113-131.
  • Havins, T.R. 1948. Celestite in Central Texas. In Rocks and Minerals, vol. 23, no. 6, p. 512
    • ---1954. In Rocks and Minerals, vol. 29, no. 78, p. 380.Hess, F.L. 1909. Texas Celestite Deposits. In The Engineering and Mining Journal, July 17,1909, p. 117.
  • Hill, R.T. 1901. Geography and Geology of the Black and Grand Prairies, Texas. U.S. Geological Survey, 21st Annual Report, pt. 7, p. 146.
  • Kunz, G.F. 1886. Notes on Some Minerals from the West. New York Academy of Sciences Transactions 5:213.
  • Phillips, W.B. 1917. Celestite Deposits in Texas. In Manufacturers Record, vol. 71.
  • Pittman, J. G. 1989. Stratigraphy of the Glen Rose Formation, Western Gulf Coastal Plain. Gulf Goast Associanon of Geological Societies Transactions 39: 247-264.
  • Simonds, F.W. 1902. The Minerals and Mineral Localities of Texas. The University of Texas Mineral Survey Bulletin No. 5, p. 17.
  • Slaughter, T.A., Ledger, E.B., and Sartin, A.A. 1987. Lithology and Strontium Distribution of the DeQueen Formation at the Highland Gypsum Quarry, Highland, Arkansas. Gulf Coast Association of Geological Societies Transactions 37:479-486.
  • Smith, A. 1989. Celestite from Bull Creek, Travis County, Texas. In Mineral News 5(4):1-2.
    • ---1990. Texas Mineral Locality Index. Unpublished paper of the Houston Gem and Mineral Society Library.
  • Stenzel, H.B., Fountain, H.C., and Kinney, D.M. 1948. Geological Resources of the Trinity River Tributary Area in Oklahoma and Texas. In University of TexasPublication 4824, pp. 72-74.
  • Taff, J.A. 1891. Reports on the Cretaceous Area North of the Colorado River. In Texas Geological Survey, 3rd Annual Report, pp. 337, 361-362.
    • Note: The Texas Mineral Locality Index was subsequently published in Rocks and Minerals.