SUPPORT US. If is important to you, click here to donate to our Fall 2019 fundraiser!
Log InRegister
Home PageAbout MindatThe Mindat ManualHistory of MindatCopyright StatusWho We AreContact UsAdvertise on Mindat
Donate to MindatCorporate SponsorshipSponsor a PageSponsored PagesMindat AdvertisersAdvertise on Mindat
Learning CenterWhat is a mineral?The most common minerals on earthInformation for EducatorsMindat ArticlesThe ElementsBooks & Magazines
Minerals by PropertiesMinerals by ChemistryAdvanced Locality SearchRandom MineralRandom LocalitySearch by minIDLocalities Near MeSearch ArticlesSearch GlossaryMore Search Options
Search For:
Mineral Name:
Locality Name:
The Mindat ManualAdd a New PhotoRate PhotosLocality Edit ReportCoordinate Completion ReportAdd Glossary Item
Mining CompaniesStatisticsUsersMineral MuseumsMineral Shows & EventsThe Mindat DirectoryDevice Settings
Photo SearchPhoto GalleriesNew Photos TodayNew Photos YesterdayMembers' Photo GalleriesPast Photo of the Day GalleryMineral Photography

Twin Peaks quarry (Rillito Cement Plant quarry; Rillito Quarry), Twin Peaks, Amole District, Tucson Mts, Pima Co., Arizona, USAi
Regional Level Types
Twin Peaks quarry (Rillito Cement Plant quarry; Rillito Quarry)Quarry
Twin PeaksGroup of Peaks
Amole DistrictMining District
Tucson MtsMountain Range
Pima Co.County

This page is currently not sponsored. Click here to sponsor this page.
Lock Map
Latitude & Longitude (WGS84): 32° 21' 20'' North , 111° 11' 26'' West
Latitude & Longitude (decimal): 32.35556,-111.19056
GeoHash:G#: 9tbbjf1sb
USGS MRDS Record:10060229
Locality type:Quarry
Köppen climate type:BSh : Hot semi-arid (steppe) climate
Nearest Settlements:
Picture Rocks9,563 (2011)5.3km
Marana41,315 (2017)9.6km
Nelson259 (2011)11.0km
Avra Valley6,050 (2011)14.9km
Tortolita4,274 (2006)17.4km

Ref.: Wilson, E.D. & G.H. Roseveare (1949), Arizona Nonmetallics, A Summary of Past Production and Present Operations, 2nd. Edition (revised), Arizona Bureau of Mines Bull. 155: 13.

Keith (1969): 389, 390, and 397.

Keith, Stanton B. (1974), AZ Bur. of Geol. & Min. Technology, Geol. Survey Br. Bull. 189, Index of Mining Properties in Pima County, AZ: 103 (Table 4).

Elevatorski, E.A. (1978), Arizona Industrial Minerals, Arizona Department of Mineral Resources, Minerals Report No. 2: 49.

Directory of Active Mines in Arizona, Arizona Department of Mineral Resources (1983), Sep. 1983.

Kupferman, S.A. (1987) The Geology of Cement Raw Materials: Pacific Southwest, in: Peirce, H.W., editor, Proceedings of the 21st. Forum on the Geology of Industrial Minerals: Arizona Bureau of Geology and Mineral Technology, Geological Survey Branch Special Paper 4: 37-43.

Phillips, K.A. (1987), Arizona Industrial Minerals, 2nd. Edition, Arizona Department of Mines & Minerals Mineral Report 4, 185 pp.

Peirce, H. Wesley (1990), Arizona Geological Survey Industrial Minerals card file.

Phillips, K.A., Beard, R.R., Niemuth, N.J., and Bain, D.R. (1991) Active Mines in Arizona – 1992: Arizona Department of Mines and Mineral Resources Directory 39, 20 pp.

Houser, B.B. (1992) (editor) Industrial Minerals of the Tucson Area and San Pedro Valley, Southeastern Arizona: Tucson, Arizona. Arizona Geological Society Field Trip, April 4-5, 1992, Guidebook, 55 pp.: 23-36.

Arizona Bureau of Mines file data.

MRDS database Dep. ID file #10060229, MRDS ID #TC10196; and, Dep. ID #10210571, MAS ID #0040190433.

A limestone and shale quarry located in South-central sec. 26, T.12S., R.11E, 2 miles NE of Avra. Owned and operated at times, or in part, by the Arizona Portland Cement Co. division of the California Portland Cement Co.

Mineralization is folded and faulted Mississippian Escabrosa, Horquilla Limestone, and Pennsylvanian-Permian Naco Group limestone. The limestone is typically siliceous and contains zones of dolomitic limestone, quartzite, and siltstone. The limestone contains sufficient silica that no additional source of silica is needed for Portland cement production. The Horquilla limestone typically consists of fine-grained, light yellowish gray limestone interbedded with shaley or silty limestone. The Escabrosa limestone consists of white to light gray limestone in the upper and middle parts of the formation and light to dark gray dolomite and limestone in the lower section. The Martin formation consists mostly of very fine- to fine-grained, laminated to thin-bedded, and medium-dark gray to olive-gray dolomite.

Workings include a quarry operation. More than 14,000,000 tons of rock have been mined for cement manufacture.

Material that is too high in silica or more than 6% MgO is crushed, sized, and sold as aggregate. The limestone is used at the Rillito cement plant, which has an annual capacity of 1.1 million tons.
The quarry is 5 miles from the plant, which is at 32-24-49N, 111-08-16W (SEC 5, T12S, R12E). Production capacity is 1.1 million short tons of cement per year. The deposit is selectively mined to produce a low magnesia, controlled-silica limestone.

Regions containing this locality

North America PlateTectonic Plate
Sonoran Desert, North AmericaDesert
No minerals currently recorded for this locality.

List of minerals for each chemical element

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on

Quaternary - Miocene
0 - 23.03 Ma

ID: 3185380
Cenozoic sedimentary rocks

Age: Cenozoic (0 - 23.03 Ma)

Lithology: Sedimentary rocks

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

Olenekian - Ediacaran
247.2 - 635 Ma

ID: 2740981
Paleozoic sedimentary rocks

Age: Neoproterozoic to Triassic (247.2 - 635 Ma)

Description: Undivided Paleozoic limestone, dolostone, quartzite, shale, and related sedimentary rocks. (248-544 Ma)

Comments: Original map source: Arizona Geological Survey, DI-8 Geologic Map of Arizona, Digital Spatial data for the Geologic Map of Arizona, v. 3.0, edited by S.M. Richard and S.M. Kneale, 2002, 10 p., 2 DOS HD disks. Arc/INFO export file (.e00) format, scale 1:1,000,000.

Lithology: Major:{limestone,dolostone,quartzite}, Minor:{shale}

Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. [133]

Data and map coding provided by, used under Creative Commons Attribution 4.0 License

This page contains all mineral locality references listed on This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.
Mineral and/or Locality is an outreach project of the Hudson Institute of Mineralogy, a 501(c)(3) not-for-profit organization. Public Relations by Blytheweigh.
Copyright © and the Hudson Institute of Mineralogy 1993-2019, except where stated. Most political location boundaries are © OpenStreetMap contributors. relies on the contributions of thousands of members and supporters.
Privacy Policy - Terms & Conditions - Contact Us Current server date and time: August 22, 2019 08:04:05 Page generated: March 29, 2019 21:55:27
Go to top of page