"There's mercury in them thar hills"
The Almaden Quicksilver area was once one of the richest mining areas in California history. What precious commodity was mined here...gold?...silver? Nope. It was mercury, in the form of cinnabar, that was mined here from the mid-1800's. The precious mercury that was extracted from the ore was used primarily in the mining of gold in California.
Why is mercury found here?
Mercury is a very rare element. It is seldomly found as a native metal and more commonly found in cinnabar (HgS), as is the case in New Almaden. Mercury ores generally occur in orogenic belts (folded and faulted land masses) where high-density rocks are forced to the surface. Hello California! You are probably starting to understand why this mercury rich ore is present in the fault-ridden Bay Area.
What does mercury ore look like?
Where mercury ores are found, they are heavily concentrated. The richest mercury ores contain up to 2.5% mercury by mass, and even lightly concentrated deposits are at least 0.1% mercury. The concentration of the mercury in the ore is apparent through the richness of the color. Ore high in mercury content bears a deep, red color. When you visit the museum, you will be able to hold a piece of high-density (very red) cinnabar. Note how heavy it is.
The mercury liquid, which is extracted through heating in excess of 1,000 degrees at which point it evaporates and is condensed, is a beautiful silver color. This is where the name “quicksilver” comes from. The density of liquid mercury is much denser than lead, making it the densest liquid on the planet. When at 100 degrees Celsius, Mercury's density is 13.35. Mercury is the only metal that during standardized conditions for temperature and pressure becomes liquid. Ask one of the curators to share a picture of a man sitting in a vat of liquid mercury at room temperature. There was no risk of him sinking due to the high density of the mercury compared to the lower density of his carbon-based frame.
Why was mercury mined here?
Long before the California Gold Rush, mercury was used in the mining and ore processing of gold. Liquid mercury reacts with gold to form an amalgam. This property was put to use in a variety of ways, most significantly “placer mining” during the California Gold Rush. Placer mining consisted of extraction of large quantities of “placer gold” that was present in the rivers of the Sierra Nevada due to the weathering of gold-quartz veins. The mercury would bind with the gold, resulting in a heavier amalgam that could be retained while lighter rock and dirt would be washed downstream. Of course, large quantities of mercury also washed downstream, which has driven high mercury levels in certain California waterways to this day. The USGS has a very good fact sheet (2005-3014) related to the mercury contamination from historical gold mining in California.
When the New Almaden Mines were expanded in 1854, the Gold Rush was well underway. The cinnabar was mined, converted to liquid mercury, and sent down the mountain in 76-lb iron flasks to a shipping dock in Alviso. The mercury traveled from Alviso up the waterways to the miners in the Sierras. During the 135 years that the seven New Almaden mines operated, over 3 million of these 76-lb flasks were shipped out, extracted from over 50-miles of tunnels honeycombing the hills of New Almaden. During this period, the New Almaden district produced more wealth than any single gold mine or any other mercury mine in the US. Mercury was also mined to a lesser extent in the Sonoma, Napa, and Lakes County regions of California.
The "S" stands for Smelly Bi-product
The process of extracting the mercury from the ore to produce the liquid mercury is a smelly one. Note that the ore is “HgS”. The “S” is sulfur. Have you ever smelled a sulfur deposit? It smells a bit like rotten eggs. There are some excellent places to experience this phenomenon in Alum Rock Park in San Jose. The processing of the ore in New Almaden resulted in sulfur gas being released into the air through smoke stacks. When the mining companies realized that the short stacks distributed the smelly sulfur fumes over the New Almaden valley and its 1,800 inhabitants, consisting of miners and their families, they redesigned the stacks to be taller, resulting in a much more convenient distribution of the smelly fumes over the hill and into San Jose. Of course, the San Jose residents were not too happy about this development.
Why is the area called New Almaden?
Cinnabar has been mined since the time of the Roman Empire. The largest and oldest known cinnabar reserves are located in the region of Almadén, Spain (Note: almadén was derived from the Arabic term meaning “the mine”). Approximately, 250,000 metric tons of mercury have been produced in that region over the past 2,000 years. When a Mexican settler discovered the large quantity of mercury ore in the hills above San Jose in the 1820’s, the region was named New Almaden after its Spanish predecessor.
Other uses of mercury
Dentistry - Mercury and silver form an amalgam used in dentistry to this day.
Native Americans and mercury - Long before the first Mexican explorers discovered cinnabar in New Almaden in the 1820’s, the Ohlone Indians ground up the mercury ore found in the region for use as pigment. Does this sound dangerous to you? Although it is broadly thought that mercury is highly toxic, this seems to be the case only if ingested or inhaled. It is quite safe to hold a piece of mercury ore. You will be happy to know this when you visit the museum and are holding the piece of cinnabar in your hand!
Hat makers and mercury - Do you remember the Mad Hatter character in Alice in Wonderland? In the mid-18th and early 19th centuries hatters used mercury in a process called “carroting”, which involved rinsing animal skins in a mercury compound, mercuric nitrate, Hg(NO3)2•2H2O. The process effectively separated the fur from the pelt, however, the solution and the related vapors were highly toxic, resulting in psychological symptoms leading to the term “mad as a hatter.”
The logging requirements:
Submit answers to 10 questions. The answers can be easily found at the New Almaden Mining Museum and along the trail up to the San Cristobal Mine. Be sure to bring plenty of water for the hike. There is no water available on this side of the park.
Please submit your answers via email. Do not post answers (except 1.A - optional) in your logs or pictures that show the objects included in the questions below. Logs submitted without responses to the questions below will be deleted.
Stage 1: New Almaden Quicksilver Mining Museum (N 37 10.711 W 121 49.166)
(Hours: Saturday/Sunday, 10-4p year-round. Fridays they open 10-4p for July/August and 12-4p the rest of the year. Call (408) 323-1107 to confirm current hours.)
The museum is housed in a building once occupied by the mining company offices. Wealthy investors also used this building for a country retreat. The curators in the museum are knowledgeable and will gladly guide you through the mercury/cinnabar exhibits in the museum, although you are also free to wander about at your leisure. Be sure to spend some time here. There are a lot of great exhibits in the museum that are certain to please rock hounds, historians and kids of all ages!
A. You can learn many interesting things through the curators and exhibits at the museum. In the write-up above, I shared a story about the diversion of the smelly sulfur fumes from New Almaden to San Jose. Share one interesting new piece of information that you learned during your visit to the museum. This answer can also be shared in your log.
B. In the mining area of the exhibit (turn to the right as you enter the museum building and walk all the way back), you can see many examples of iron ore. Near the windows, there is a glass case that includes a large map and examples of ore mined in Almaden Quicksilver County Park. Near the top of the case on the right side, there is a fist-sized piece of dark-red cinnabar. What nickname is shown in quotes below the word cinnabar?
C. In the glass case in the middle of the room, you can find some interesting items made from cinnabar. What items are directly behind the “Cinnabar Ware” sign and who made them?
D. The flasking exhibit notes that New Almaden mercury was considered to be superior. What was painted on the side of the flasks in white paint to identify this superior product?
Stage 2: Rotary Furnace (hike required; N 37° 10.475 W 121° 50.659, park at N 37 10.520 W 121 51.702) - The onset of WWII led to renewed interest in New Almaden due to the use of mercury in munitions. This continuous furnace was created to increase the rate at which the mercury could be extracted from the ore. There is an informational plaque located at this waypoint.
A. To what temperature did the furnace heat the ore?
B. What two gases were created in the process?
C. What two animals are included in the top left and right hand corners of the plaque?
Stage 3: San Cristobal Mine (continuation of Stage 2 hike, N 37° 10.706 W 121° 50.825) Directly below your feet there are still veins of cinnabar among miles of tunnels, some as far as 2,000 feet down.
The County long ago sealed up all known tunnels in New Almaden. The San Cristobal Mine can be entered for about 200 feet. After a long, hot hike, you will enjoy this cool refuge.
A. Near the cords, there is a very large square block of another indigenous California rock with notches cut into it. What is it?
B. Do you see any cinnabar on the site? Is this consistent with your expectations?
C. How many bolts hold the sign above the mine in place?
I hope you enjoyed learning about Mercury and its role in the development of New Almaden!
Special thanks to the curators/rangers at New Almaden and to sammydee for making this Earthcache possible.
Congrats to WERDAVE, CissyPSP, PAVEIT, and Geokashers on the FTF!