Skyline Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (City Hall Loop)

I’ve worked in the oil & gas industry in Downtown Houston for over 15 years.  Like many others, every day I walk past buildings covered in lovely rocks, minerals, and fossils without a second thought.  Though we may not have mountains in this part of the state, we have a stunning skyline, and I will take these beauties for granted no more!  After the most recent Texas Parks and Wildlife Becoming an Outdoors Woman workshop that my friend and I teach geology for twice a year, the idea of creating a downtown walking tour sparked.  We enlisted a fellow geoscientist also located in Downtown Houston to join us in our quest.  We found a few scattered tours and information online (referenced below), an e-book on Amazon (link below), and little else.  So Katy, Christen, and I have set out twice a week to scout all of Downtown Houston before triple digit temperatures prevent us from leaving the comfort of our air-conditioned offices.

We’ve taken hundreds of pictures and have tried to find as many facts and best guesses as possible.  If you do one of our self-guided tours on your own and find more accurate information, we’d be happy to update it here.  We proudly bring to you the first of several self-guided walking tours: City Hall Loop.  There’s a condensed free PDF guide at the bottom of this post for easy printing or smart phone viewing.  And if you need a super quick geology precursor, you can find that here: Geology Basics: For the Casual Observer or Amateur Enthusiast.  Enjoy, fellow rock lovers!

WELLS FARGO – 1000 LOUISIANA

Building Base

Larvikite (intermediate igneous)

Specific variety of Monzonite, for thumbnail-sized feldspar

From Larvik Batholith in the Oslo Rift in Norway (Permian, 292-298 my) or Killala Lake Alkalic Rock Complex near Thunder Bay in Ontario, Canada

Could be confused with Ubatuba (I did)

Pavement/Accent Stone

Granite (red/pink, felsic igneous)

Poikilitic texture

Fun Fact

The Wells Fargo Plaza is currently the 20th-tallest building in the United States, the second tallest building in Texas and Houston, after Houston’s JPMorgan Chase Tower, and the tallest all-glass building in the Western Hemisphere

Building Base

Distinguishing and observed features: alkali and plagioclase feldspars, blue labradorescence

Pavement/Accent

Poikilitic texture: large component crystals (feldspar, in this case) contain smaller crystals of other minerals within them, most easily observed in petrographic thin sections

Observed: Potassium feldspar, smoky quartz, biotite, hornblende, pyroxene

HOUSTON PUBLIC LIBRARY – 500 MCKINNEY

Building

Granite (dark pink, felsic-intermediate igneous)

From South Dakota

Contains xenoliths and pegmatite veins

Xenoliths: a foreign (identifiably different from the rock it is within) rock fragment enveloped by a larger rock, a magmatic inclusion that occurred during magma emplacement (in this case)

Observed: xenoliths ranging in size from Katy’s hand to Katy’s head, contact metamorphism around rim

Pegmatite veins: holocrystalline (roughly), intrusive igneous rock composed of interlocking phaneritic crystals (usually larger than 1”)

1. Pyroxene (~90 degree angle)
2. Pegmatite veins
3. Hornblende (~120 degree angle)

Observed: potassium feldspar rich veins and dark mineral veins, contains both pyroxene and hornblende

HOUSTON CITY HALL – 901 BAGBY

Pavement/ Corner Stone

Oolite (marine sedimentary)

Bedford Oolite from Bedford, Indiana (quarry)

Salem Limestone (geo)

Mississippian (358-323my)

Also found in Indiana University

Building/Pool

Fossiliferous Limestone (marine sedimentary)

Cordova Shell from Austin (quarry/trade)

Whitestone Lentil (geo)

Walnut Formation

Middle Cretaceous (105my)

Also found in the National Museum of Natural History in Washington D.C.

Building/Pool

1. Trigonia, Turitella, Crinoid
2. Rudist
3. Trigonia
4. Rudist, Bryozoan
5. Trigonia, Turitella, Bryozoan

Pavement, etc.

1. Worm trail
2. Crinoid
3. Festoon trough-cross bedding
4. Bryozoan (Fenestella plate?)
5. Crinoid, Bryozoan

ONE SHELL PLAZA – 910 LOUISIANA

Building/ Pavement

Tufa (Travertine, continental sedimentary)

Travertino Romano (trade) from Tivoli near Rome in Italy

Also known as Romano Classico or Travertine Classico and Travertino Romano Antico (darker varieties)

Building, pavement, cornerstones, and accent stones all travertine

Tufa/Travertine: formed by algae/calcium carbonate in hot springs, phytoherms (freshwater reefs) and thrombolite-stromatolites; not to be confused with tuff/tufo (igneous)

1. Stroms
2. Alternating Travertino Romano Classico and Travertino Romano Antico
3. Vugs

Observed: stromatolite patterns/precipitation growth dominant feature, some vugs partially to fully filled with more transparent cement

LANIER PUBLIC WORKS – 611 WALKER

Building

Gneiss (high grade metamorphic)

Foliation of light and dark minerals in large bands

TWO SHELL PLAZA – 811 LOUISIANA

Building

Tufa (Travertine, continental sedimentary)

Identical to One Shell (see One Shell for details)

Building Base

New façade (<5yrs)

Diabase/ microgabbro (mafic intrusive igneous)

Lower Jurassic (201-174my)

Virginia Mist Granite (trade) from Canada

Also found in Jet Mist Quarry in Rapidan, Virginia

Diabase/microgabbro: dark-gray mosaic of elongate plagioclase crystals and clinopyroxene, with some masses characterized by olivine or bronzite

Pavement

Best guess: slate (low grade metamorphic)…but most likely phyllite (low-medium grade metamorphic) as micas were observed

ESPERSON BUILDINGS – 808 TRAVIS

Niels Tower

Oolite (marine sedimentary)

Built in 1926 by Mellie Esperson

Bedford Oolite from Bedford, Indiana (quarry)

Salem Limestone (geo)

Mississippian (358-323my)

Also found at Houston City Hall

Cornerstone, Accents, and Base

Granite (light-pink felsic intrusive igneous)

Town Mountain Granite from Austin and Llano Uplift

PreCambrian (>1.37-1.23gy)

Fun Fact

The only complete example of Italian Renaissance in Downtown Houston

Mellie Tower

Oolite (marine sedimentary)

Built in 1941 by Mellie Esperson

Bedford Oolite from Bedford, Indiana (quarry)

Salem Limestone (geo)

Mississippian (358-323my)

Also found at Houston City Hall

Cornerstone, Accents, and Base

Gabbro (mafic intrusive igneous)

Fun Fact

Intentionally built to not be as tall or as ornate as Niels Tower

Joined with Niels Tower on all but 2 floors

Mellie Tower

Gabbro: coarse-grained, dark-colored, intrusive igneous rock, usually black or dark green in color and composed mainly of the minerals plagioclase and augite

Cornerstone: Contains Esperson Nordic Crest

Oolite: See Houston City Hall Pavement, contains worm trails (red)

Niels Tower

Town Mountain Granite: Coarse-grained, pink, quartz-plagioclase-microcline rock, in part porphyritic with large microcline phenocrysts. Occurs in plutons up to 13 mi in size that tend to be concordant circular vertical cylinders with concentric textural variations; boundaries range from sharp and regular to highly irregular with wide zones of mixed rock. Makes up Enchanted Rock granite mass, Gillespie and Llano Counties.

Observed: zoned and rapakivi feldspars, poikilitic texture

Poikilitic texture: large component crystals contain smaller crystals of other minerals within them, most easily observed in petrographic thin sections

Rapakivi: large rounded crystals of orthoclase each surrounded by a rim of oligoclase (a variety of plagioclase)

1. Poikilitic texture
2. Rapakivi
3. Zoned feldspars

Oolite: sedimentary rock formed from ooids, spherical grains composed of concentric layers

919 MILAM (WITH THE STARS)

Red Base

Granite (felsic intrusive igneous)

Original (?): Coldsprings Bright Red Granite from Milbank in South Dakota (trade)

Resurfaced (?): Radiant Red Granite from Bear Mountain near Fredericksburg (trade)

Radiant Red from Llano Uplift

PreCambrian (>1.37-1.23gy)

Fun Fact

Renovated in 2006

The first of three buildings in Downtown Houston to be networked in the first phase of a pedestrian tunnel system

Pink Columns

Granite (felsic intrusive igneous)

Coldsprings Dakota Mahogany Flame from Milbank in South Dakota (trade)

Could be from the same quarry as Houston Library (next two slides show similar xenoliths to Houston Library)

Accents

Gabbro (mafic intrusive igneous) and Aluminum stars

Xenolith: a foreign (identifiably different from rock it is within) rock fragment enveloped in a larger rock, a magmatic inclusion that occurred during magma emplacement

Observed: stray fractures/dike/veins filled with dark, fine-grained or glassy material

TRAVIS PLACE – 1010 TRAVIS

Building Base and Pavement

Granite (felsic intrusive igneous)

Color/texture match to Sunset Red Granite from Llano uplift in Texas

Phaneritic/ poikilitic pink granite with large rapakivi feldspars and dark mineral clusters

Poikilitic texture: large component crystals contain smaller crystals of other minerals within them, most easily observed in petrographic thin sections

Rapakivi: large rounded crystals of orthoclase that are surrounded by a rim of oligoclase (a variety of plagioclase)

KINDER MORGAN – 1001 LOUISIANA

Pavement (light grey)

Granite (light grey felsic-intermediate intrusive igneous)

Color matched: Coldspring Rockville (trade)

From East-Central Batholith in Rockville, Minnesota (assumed)

PreCambrian (1.78gy)

Coldspring Rockville Granite: granite (quartz 20-60% and plagioclase 10-65%) to granodiorite (quartz 20-60% and plagioclase 65-90%)

Poikilitic texture: large component crystals contain smaller crystals of other minerals within them

Observed: large feldspars with poikilitic texture containing dense, dark minerals in almost every slab

Steps (dark grey)

Granite (dark grey felsic-intermediate intrusive igneous)

Color matched: Coldspring Lake Superior Green (trade)

From East-Central Batholith near Isabella, Minnesota (assumed)

Late Archean (2.8-2.5gy)

Coldspring Lake Superior Green: could be granite, granophyre, ferro-monzodiorite, or leucogabbro…challenging anyone to stick their nose to the rock and give us a more educated guess

Observed: uniform and equal amounts of salt and pepper

Pavement/Accent Stone

Granite (pink felsic intrusive igneous)

Color matched: Sunset Red Granite from Texas (trade)

From Granite Mountain near Marble Falls in Texas (assumed)

PreCambrian (>1.37-1.23gy)

Could be same stone as Texas State Capitol Building in Austin

Town Mountain Granite: Coarse-grained, pink, quartz-plagioclase-microcline rock, in part porphyritic with large microcline phenocrysts. Makes up Enchanted Rock granite mass, Gillespie and Llano Counties.

Observed: contains rapakivi and poikilitic feldspars

Fun Fact

Due to downtown Houston’s diagonal street grid, all four sides of the Kinder Morgan building are exposed to the sun

Download Free PDF Skyline Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (City Hall Loop) here: DowntownGeologyCityHallPDF

Published Walking Tours

Skyline Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (City Hall Loop)

Tunnel Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (Red Loop)

Skyline Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (Hyatt Loop)

Tunnel Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (Yellow Tunnel)

Skyline Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (Jones Loop)

Tunnel Geology: A Self-Guided Walking Tour of Downtown Houston’s Buildings (Teal Tunnel)

CONTRIBUTORS

Sheila Echols-Smesny holds a Bachelor of Science in Geology from Sam Houston State University, an Executive MBA from Texas Woman’s University, and works at an oil & gas company in Houston.  Red Shoes. Red Wine. is Sheila’s travel, lifestyle, & hobby blog.

Christen Peevy holds a Bachelor of Science in Geology from University of Oregon and works at an oil & gas company in Houston.  Christen’s lifestyle blog is Short Sweet & Lovely.

Katy Mainwaring holds a Bachelor of Science in Geology from Texas Tech University and works at an oil & gas company in Houston.  Katy teaches geology with Sheila for Texas Parks and Wildlife Becoming an Outdoors Woman program.

BEFORE YOU GO

Safety

• Look up, not at your phone, when navigating downtown
• Please be mindful of the traffic lights, pedestrian signals, bike lanes, and buses
• Buses make frequent stops and can sometimes hop curbs
• Some curbs, pavements, and streets may be uneven

Etiquette

• Please review the walking guide prior to arriving downtown to maximize time spent on the tour
• Please be mindful of downtown employees and keep slower pedestrian traffic to the right so they can go about their business
• Try to walk in pairs if walking around downtown as a group
• If approached by a homeless person, try to be firm but respectful

REFERENCES

• Houston Geological Society, 1995, Walking Tour of Downtown Houston Building Stones: Research Committee, Philip W. Porter
• Houston Gem and Mineral Society, Houston Geologic Society, 2008, Walking Tour – Houston Building Stones, Neal Immega
• Fossils in the Architecture of Washington, D.C.: http://dcfossils.org/index.php/gallery11/#origins
• United States Geological Survey: https://mrdata.usgs.gov/geology/state/map-us.html
• Wikipedia
• Geology.com

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