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California Stone Industry (historical account up to circa 1950)

Excerpts from

Geologic Guidebook of the San Francisco Bay Counties:
History, Landscape, Geology, Fossils, Minerals, Industry,
and Routes to Travel, Bulletin 154

Olaf P. Jenkins, Chief, California Division of Mines,
San Francisco, California, December, 1951.

(Used with permission, California Department of Conservation, California Geological Survey.)

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California Dimension Stone

"Stone has long been one of northern California's principal mineral products; but during the last 50 years the demand for dimension stone (produced in specified shapes) has dropped sharply, while the demand for crushed stone has correspondingly increased. This trend has been caused chiefly by the widespread acceptance of concrete as a material in paving and heavy construction work. Most of the deposits that were formerly operated as dimension stone sources cannot be profitably worked for crushed stone, but some are still producing stone for use as architectural decorative materials and monuments. In northern California dimension stone has been obtained principally from granite quarries in the Sierra Nevada; from basalt quarries in Napa, Sonoma, Solano, and Santa Clara Counties; from limestone quarries in El Dorado, Santa Cruz, and Tuolumne Counties; and from sandstone quarries in Colusa and Santa Clara Counties.

Volcanic Rocks Useful in the San Francisco Bay Area, by C. W. Chesterman, Associate Mining Geologist, California State Division of Mines.

"Volcanic rocks in the San Francisco Bay area - lava flows, beds of tuff, agglomerate, and breccia - range in age from late Jurassic to late Tertiary. They are well exposed in almost all of the bay counties and cover extensive areas in Alameda, Contra Costa, Napa, Solano, and Sonoma Counties.

"Numerous quarries in Marin, Napa, Solano, and Sonoma Counties that formerly furnished paving and building blocks now supply huge quantities of crushed stone for concrete aggregate and road metal. The demand for lightweight aggregate has increased the output of pumice from the tuffs, which formerly were quarried for building blocks. The rapid growth in the use and demand for expanded perlite as an industrial material, especially in the fields of lightweight aggregate, has developed much interest in this glassy volcanic rock.

"Various volcanic rocks, especially the rhyolites which have the property of splitting readily along well-defined parting planes, are quarried at several places and sold as flagstone and colored building stone.

"Types of Volcanic Rocks. There are several varieties of volcanic rocks in the San Francisco Bay area, ranging from basalt to rhyolite. Large areas are underlain by the older basaltic rocks of the Upper Jurassic Franciscan formation. Still larger areas are underlain by Tertiary and Quaternary volcanic rocks comprising a varied assortment of rhyolites, andesites, basalts, tuffs, agglomerates, breccias, and glasses. These rocks are described briefly in order of their decreasing silica content.

"Perlite is a glassy volcanic rock, characterized by a so-called onion-skin fracture, and capable of breaking down into spherical fragments, many of which have a pearly luster. For a volcanic rock, a rather large amount of water enters into its composition. Perlite ranges in color from light to dark gray; some of it is reddish. When rapidly heated, perlite as well as many other volcanic glasses, expands into a frothy, white, pumice-like material which is of value as a light-weight aggregate in the building industry.

"Obsidian is a glassy volcanic rock having a conchoidal fracture and the luster of common glass. Although usually black in color, obsidian may be red, brown, gray, or even greenish. Some of it is banded, owing to the concentration in layers of very small magnetite particles and embryonic crystals. An obsidian that contains appreciable amounts of quartz and feldspar usually is referred to as a vitrophyre.

"Another variety of volcanic glass, pitchstone, differs from obsidian in that it has a pitchy luster, a subconchoidal fracture, and contains considerably more water (2 to 8 percent) than obsidian.

"Pumice is a cellular volcanic glass formed by rapid expansion of gas contained in solidifying acidic lava. Most of it is light gray to white in color and occurs in tuffs or other pyroclastic rocks. The latter are made up of fragmental volcanic materials expelled from volcanic vents and deposited upon a land surface or in standing water.

"Rhyolite is a common type of acidic volcanic rock in the San Francisco Bay area. It is multi-colored, normally has a porphyritic texture, and generally is characterized by phenocrysts or crystals of quartz, sanidine (a glassy variety of orthoclase), and biotite in a groundmass of minute crystals and volcanic glass. Many of the rhyolites show well-developed banding or flow structure, which developed while the rock was in a molten condition.

"Trachyte, which occurs rarely in the San Francisco Bay area, is a light-colored rock resembling rhyolite. It has a porphyritic texture and contains phenocrysts of sanidine enclosed in a groundmass of small feldspar crystals. Quartz is normally absent. Hornblende and biotite are present and usually occur in well-developed phenocrysts.

"Most dacite is light colored, ranging from gray through yellowish-brown to pink. Dacite is porphyritic and contains phenocrysts of plagioclase, hornblende, biotite, quartz, and sometimes hypersthene, enclosed in a groundmass of small crystals and glass.

"Andesite is one of the most abundant volcanic rocks in the bay area. It differs slightly from dacite in containing little or no quartz. Most andesites are either dense and compact or else porphyritic. The porphyritic varieties contain phenocrysts of plagioclase, hornblende, and biotite enclosed in a fine-grained ground-mass of needle-like crystals of feldspar, with or without glass. Most of the rock is dark gray and may easily be mistaken in the field for basalt.

"Basalt is also common in the bay area. It is a dark, dense rock ranging in color from greenish gray or brown to black. Porphyritic varieties are common, though the phenocrysts may be masked by the dark groundmass. With the aid of a hand lens, the constituent minerals can be recognized. Most of the phenocrysts are green and greenish-black olivine, black prismatic crystals of hornblende and augite, black platy crystals of biotite, and dark-appearing crystals of plagioclase set in a fine-grained aggregate of lath-shaped feldspar crystals and tiny prismatic crystals of augite. Jointing in many basalt flows is platy or columnar. Flow structures are common, as are cavities more or less filled with calcite, chalcedony, or some variety of zeolite.

"Tuff is a fine-grained, fragmental volcanic rock. It is made up of various types of volcanic material such as pumice, pumicite, rhyolite, andesite, and basalt, which have been expelled in the air from volcanic vents and deposited upon a land surface or in standing water. Tuffs may be either loosely consolidated or compact. In places they contain sufficient amounts of pumice to warrant mining as light-weight aggregate. Several of the more compact varieties of tuff in Napa and Sonoma Counties were formerly quarried for building blocks.

"Fragmental volcanic rocks expelled from volcanic vents, but coarser than tuff, are called breccia or agglomerate. If the fragments are predominantly angular the rock is called a breccia; if the fragments are rounded it is called an agglomerate. In both types, however, the fragments consist essentially of various kinds of volcanic rock with minor amounts of non-volcanic rocks such as granite, limestone, sandstone, and shale torn from the vent walls.

St. Helena Church, St. Helena, Napa County. Cresta Blanca Winery, north of St. Helena, Napa County
Fig 1. St. Helena Church, St. Helena, Napa County. Constructed in 1879 of ryholite, andesite, and dacite. Fig 2. Cresta Blanca Winery, north of St. Helena, Napa County. Gate is made of field boulders of andesite and basalt.
The Cresta Blanc Winery, North of St. Helena, Napa County Stone fence on Silverado Trail, east of Yountville, Napa County
Fig 3. The Cresta Blanc Winery, North of St. Helena, Napa County. constructed in 1889 of dacite and rhyolite blocks. Fig 4. Stone fence on Silverado Trail, east of Yountville, Napa County. Built of field boulders of andesite, dacite and rhyolite.
Napa Creek Bridge, northeast of Zinfandel, Napa County.
Fig 5. Napa Creek Bridge, northeast of Zinfandel, Napa County. Constructed in 1913 of perlite rock, dacite, and rhyolite. (According to a Napa County resident, the waterway over which the above bridge is located is over the Napa River - rather than Napa Creek. The bridge is located on Zinfandel Lane .)


"Older Volcanic Rocks. The oldest volcanic rocks exposed in the San Francisco Bay area are the basalts, diabases, tuffs, and breccias of the Upper Jurassic Franciscan formation. For the most part, these rocks are so badly altered that they are easily mistaken for silicified shale or sandstone. Most of them are dark colored and fine grained, except for some coarse-grained porphyritic varieties of basalt.

"One of the most interesting of these older volcanic rocks is the pillow basalt, a name applied to a lava which solidified, probably under water, in piles of pillow-like or bulbous bodies. The pillows range in size from a few inches to several feet in diameter, and many are indented. Pillow basalts are closely associated with the red cherts of the Franciscan formation. Good examples are exposed at Hunters Point in sea cliffs at Point Bonita; along Highway 101 about half a mile north of the Golden Gate Bridge; and in the canyon of Lagunitas Creek, about 5 miles east of Point Reyes.

Fig 3. Pillow basalt in the Franciscan formation exposed along the Arroyo San Antonio, Marin County. Lava of similar appearance is well exposed in road cuts 1.1 miles north of the end of Golden Gate Bridge. Pillow-shaped joints probably were caused by contact of molten lava with water. Pillow basalt in the Franciscan formation exposed along the Arroyo San Antonio, Marin County

"Vesicular and amygdaloidal basalts are also interstratified with sedimentary rocks of the Franciscan formation. Many of these are greatly decomposed and form inconspicuous masses. Basalt in the form of a sheet is well exposed on the flanks of Cahil, Sawyer, and Sweeney Ridges, San Mateo County. Several other good exposures can be found in Marin County, especially north of Mount Tamalpais. Basalt and diabase also occur as intrusive plugs and dikes, which cut the sedimentary rocks of the Franciscan formation. Several of these intrusive bodies occur in Marin, San Francisco, and San Mateo Counties.

"Younger Volcanic Rocks. Although some evidence of Eocene volcanism is presented by glass (tuff) shards in diatomite of the Markley formation, the earliest indication of widespread volcanic activity in the Tertiary period in the San Francisco Bay area is shown by the presence of Miocene lavas in the vicinity of the New Almaden mine; along the crest of the Santa Cruz Mountains between Pilarcitos Creek on the north and the Santa Clara County boundary on the south; and in the hills west of the Stanford University campus. The New Almaden district lavas are flows of rhyolite or dacite; the Santa Cruz Mountains examples consist of diabase dikes, thin basalt flows, and a few beds of tuff; and the volcanics west of the Stanford campus are largely flow basalt. Miocene basalts are commonly amygdaloidal; the vesicle fillings may be calcite, chalcedony, quartz, analcite, serpentine, or even petroleum.

"The Pinole tuff is probably the oldest Pliocene volcanic rock exposed in the bay area. In most places it consists of stratified tuff composed of white to yellowish-white pumice ranging from dust-sized particles to fragments as much as 2 inches in diameter; the tuff is commonly interstratified with beds of poorly consolidated sand and gravel. The presence of andesite, fragments and a general lack of quartz indicate that it is andesitic in composition. The rock is well exposed along the shore of San Pablo Bay between Rodeo and Oleum and in road cuts along Highway 40 west of Pinole.

Fig 29. A typical exposure of Pinole tuff (Pliocene) on San Pablo Bay half a mile west of Oleum, Contra Costa County. Volcanic ash layers are interbedded with sandy strata and lenses of coarse fragmental white pumice. Camera Facing northeast. Carquinez Strait is behind the nexk of land. A typical exposure of Pinole tuff (Pliocene) on San Pablo Bay

"A tuff similar to the Pinole and of approximately the same age is exposed in Lawlor Ravine in the southwestern corner of Antioch quadrangle. Because it is found on the Great Valley side of the Coast Ranges it is considered a separate formation, and has been named the Lawlor tuff.

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