Spending the past few days in San Francisco with a busy schedule, I'd anticipated this would be the first week since launching Mineral Bliss last February that there wouldn't be a post. It was a pleasant family oriented trip, however, into which my son Alex and I were able to squeeze in a few hours for a hike. As we scanned his trail book to pick one, I saw "semi-precious stones" mentioned in conjunction with the "Rodeo Beach Hike." Parking to reach the trail was directly at Rodeo Beach. We drove there and headed out, making it approximately two hundred yards to near the shoreline. Thereafter, we were rarely off our knees.The picture atop this page is of pebbles ranging in size from about five millimeters to one and a half centimeters. It includes a number of less common pebbles that I'm reluctant to identify without help. Most of what's green is serpentine from the serpentinite rocks abundant in the adjacent Marin County headlands. These headlands are also rich in chert that can be gray, green, red, blue, or brown.
Other beaches along San Francisco Bay yield similar pebbles. Pictured at left are a few that my son Alex picked up several months ago across the Bay at Baker Beach, which is within the San Francisco city limits. I first suspected that the red and brown pebble at center right could be an agate, but am now convinced that it's chert or possibly jasper. One of Marin County's beaches is known as Agate Beach. From the Web, I'm told that many grains of sand there are from agates, but that marine fossils are a better bet for collecting than agate.
Serpentinite pebbles from both Rodeo Beach and Baker Beach remind me of the "jade" that I recall checking out years ago at Jade Beach along the Pacific a couple hundred miles south in the Big Sur. At Jade Beach, the stones are are much larger. Some are actually boulders. They are said to be jadeite and/or nephrite. I'd enjoy the opportunity to compare the Jade Beach material with some of these pebbles.
Serpentinite pebbles from both Rodeo Beach and Baker Beach remind me of the "jade" that I recall checking out years ago at Jade Beach along the Pacific a couple hundred miles south in the Big Sur. At Jade Beach, the stones are are much larger. Some are actually boulders. They are said to be jadeite and/or nephrite. I'd enjoy the opportunity to compare the Jade Beach material with some of these pebbles.
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