Rock Picture of the Week Archive 7

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Orbicular Granite

Photo by Larry Martin

This type of Granite is rare. The orbs vary a lot in size and shape.
The experts do not all agree on how they were formed, but the most favored theory is that material deposited and grew around a solid particle as they cooled.

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 Short-Faced Bear

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Selenite

Photo by Jim Bryan
From the private collection of Mike & Chris Whittier of Rocks in a Hard Place.

Selenite (CaSO4-2H2O) is often precipitated out of mineral rich water. This specimen came from the Giant Crystal Cave in the Niaca Mine, Mexico. This cave has the world's most spectacular Selenite crystals, with crystal faces more than a yard wide and 10 yards long. The cave appears like a scene right out of a science fiction movie.

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Smilodon

Photo by Larry Martin
Courtesy of the Fossil Discovery Center Of Madera County

Saber-toothed Cat
Smilodon fatalis
The Saber-tooth cat is California's official state fossil.

This fierce predator was about 4-5 feet long and 3 feet tall and weighed from 160 to 280 kg. (350 to 620 lbs.). It was about the same size as the modern lion, but shorter and more massive. Smilodon is most famous for its 8-inch long canine teeth. This "saber-tooth" characteristic was common to many species of prehistoric cat, including another Fairmead site species, Scimitar cat (Homotherium serum). The Felidae (cat) family evolved in the forests of Eurasia 40 million years ago. The early predecessors Smilodon migrated from Asia 8.5 million years ago. Smilodon fatalis existed from 1.5 million to 9,400 years ago, when it became extinct

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Crazy Lace Agate

Photo by Jim Bryan
From the private collection of Mike & Chris Whittier of Rocks in a Hard Place.

Crazy Lace Agate (SiO2) is named for random lace-like patterns in the Agate layers. Most of this material is white or gray, but brown, red, and yellows are fairly common. The layers are sometimes porous enough that artificial colors can be added.
This, and most of the available material, comes from Mexico.

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Ground Sloth

Photo by Larry Martin
Illustration by Dorothy S. Norton
Now on display at the Fossil Discovery Center Of Madera County

Harlan's Ground Sloth
Paramylodon harlani

Harlan's Ground Sloth was the most numerous of Fairmead's 3 ground sloths. An adult Harlan's sloth was about 12 feet in length, standing approximately 6 feet high, and weighed 3,500 pounds. This very large animal was a grazer, feeding primarily on grasses.
Paramylodon had front claws 8-12 inches long used for digging roots and, if necessary, defense. The earliest predecessors of the sloth family appeared in South America during the Paleocene epoch, 60 million years ago. These animals evolved and diversified over time. About 3.5 million years ago, North America and South America were joined together by the formation of the Isthmus of Panama. Several species of large ground sloths migrated to North America, while the smaller tree-dwelling members of the sloth family remained in South America. The other two giant sloths present at the Fairmead site are the Shasta ground sloth, Nothrotheriops shastensis, and Wheatley’s ground sloth, Megalonyx wheatleyi. The various ground sloths of North America that became extinct less than 10,000 years ago.

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Apatite

Photo by Jim Bryan
From the private collection of Mike & Chris Whittier of Rocks in a Hard Place.

Apatite (Ca5(PO4)3(Cl,F,OH)) is a group of minerals consisting mainly of Chlorapatite, Fluorapatite, and Hydroxylapatite, that grade into each other. It is a major part of bones and tooth enamel.
Commercially it is mined as a source of phosphorus for fertilizer, and sometimes as a gemstone.

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Horse

Photo by Larry Martin
Illustration by David Douglas
Courtesy of the Fossil Discovery Center Of Madera Co

Prehistoric Horses in North America

Larry Martin
San Joaquin Paleontology Foundation

    Among the many species found at the Fairmead site, horse fossils are quite common.  This is not extraordinary given that horses evolved in North America.  Their fossil history is well documented in the North American fossil record.
    During the early Eocene Period (53 million years ago), dawn horse roamed the forests of America.  Dawn horse, Eohippus, was no larger than a small dog, 10-20 inches in height.  The teeth of this small mammal reveal that it fed primarily on fruit and soft plant materials.  Unlike modern ungulates (hoofed mammals), Eohippus possessed 4 toes on the front legs and three on the hind legs.  Modern horses are ungulates classified in the order Perissodactyla, odd toed mammals with a single predominant hoof.
    During the rest of the Eocene Period (55 to 34 million years ago) species from Orohippus to Epihippus developed teeth and body parts that marked the beginning of a transition from forest browsers to grassland dwellers. These small animals developed more flattened teeth to enable it to browse tougher plant material.  This enabled them to feed on a wider variety of plants.  Their body size slowly increased with improved diet.  These early horse predecessors still had feet with pad-footed toes, somewhat like a dog, in order to move around soft forest floors.
    During the late Eocene Period (37 to 32 million years ago), the climate of North America became drier.  Forests were diminishing and evolving grasses were filling the plains. The evolution of horses and other grazing ungulates paralleled the expansion of grasses.  Primitive horses responded by exhibiting characteristics of modern horses.  The Middle Horse, Mesohippus, marked a significant point in horse evolution.  These horses were approximately 24 inches high at the shoulder with straight backs.  They had longer necks and narrower heads than previous species.  Its teeth were broader and tougher.  The legs of Mesohippus were longer and stronger with a middle toe had formed into a pad, which foreshadowed the hoof.  These prairie-dwelling horses became longer-legged and extremely swift, enabling it to elude predators.  Their teeth evolved further to cope with the highly erosive silica content of grasses.  Horses adapted from browsing to grazing on a diet almost entirely of grasses.
    Beginning with the emergence of Parahippus, 23 million years ago (early Miocene), and extending to the horse, genus Equus, 4 million years ago (early Pliocene), horses continually evolved.  During this period of time, several dozen species evolved.  Two of these species are thought to be present at the Fairmead dig site.  The most common of these is similar to Western Horse, Equus occidentalis.  
    The history of the horse in North America is somewhat of an odyssey.  About 2.5 million years ago one or more of these species crossed the Bering Land Bridge into Asia, Europe, and Africa; providing the forbears of modern horses.  Even though they originated in North America, they became extinct here about 8,000 years ago.  Climate changes, primarily drought following the ice ages, are considered to be the major factor.  Later, as a more evolved species, they were re-introduced by Spanish explorers in the early sixteenth century.

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Topaz

Photo by Jim Bryan
From the private collection of Mike & Chris Whittier of Rocks in a Hard Place.

Topaz (Al2(F,OH)2SiO4)  can appear in many colors and makes a fine gemstone.
This specimen came from the Thomas Range in Utah, and is the Utah State gemstone.

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Ammonites

Photo by Jim Bryan
From the private collection of Mike & Chris Whittier of Rocks in a Hard Place.
Illustration by Nobu Tamora

Ammonites are extinct cephalopods that died out with the dinosaurs. Their closest living relatives are the octopus, squid, and cuttlefish.
There were many varieties of them and some grew to 3 yards in diameter. In some areas the fossils have a strong iridescence which is sought after by collectors and jewelers.

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Sphalerite and Galena on Calcite

Photo by Jim Bryan
From the private collection of Mike & Chris Whittier of Rocks in a Hard Place.

Sphalerite ((Zn,Fe)S), brownish mineral, is the major ore of Zinc. Galena (PbS), silver color, is the major ore of lead.
Together with Calcite (CaCO3), white crystals, they make an attractive addition to any collection. This specimen came from Tennessee.

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Chiastolite

Photo and information by Larry Martin

Chiastolite is a unique variation of the mineral andalusite, an aluminum silicate (Al2SiO5). The mineral belongs to the orthorhombic system and occurs as prismatic crystals with nearly square cross sections. Andalusite has a hardness of 7.5 and a specific gravity of 3.15-3.2. It has a vitreous luster and white streak. Andalusite occurs as porphryroblasts resulting from contact metamorphism of argillaceous sediments. It also occurs in regionally metamorphosed schists. It is frequently associated with kyanite, sillimanite and staurolite.
Chiastolite forms when carbonaceous or clay inclusions are incorporated in andalusite during crystal formation. These inclusions form a characteristic cross that prompts the name of this particular mineral form. Exceptional chiastolite crystals have been observed with a diameter exceeding 1 1/2 inches and lengths exceeding 8 inches; however, specimens this size are quite rare. Colors typically vary from brown to tan, blue-gray to gray, green, white, and pink.
Chiastolite is often fashioned as an opaque gem. When fractured or cut perpendicular to the long axis the cruciform pattern is exposed. The pattern may change along the length of a single crystal. The material is easily worked into a cabochon cut due to its softness and is often made into earrings, necklaces, rings, and broaches.

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Fluorite

Fluorite (CaF2) is one of mineral collector's favorites because of its often large, colorful crystals that also glow in UV light. Fluorite appears in a wide variety of colors, but is too soft to make durable jewelry.
This specimen comes from China.

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Dire Wolf

Photo and information by Larry Martin
Illustration by David M. Douglas

Dire Wolf

Canis dirus

 

The family Canidae (dog-like mammals) originated in North America and Europe during the Eocene Epoch about 40 million years ago. Mammals of the genus Canis containing dogs, wolves, and coyotes, were present in North America 6 million years ago, during the Miocene Epoch. The dire wolf was a more robust animal than the modern gray wolf, Canis lupus. Dire wolves were about 5 feet in length and weighed 130 to 190 pounds. Evidence indicates that dire wolves and modern wolves shared similar social and behavioral traits. Cooperative hunting strategies allowed these wolves to become formidable predators of large Pleistocene animals. Dire wolves and modern grey wolves coexisted in America prior to the extinction of the dire wolf about 10,000 years ago. The dire wolf fossil at the Fairmead Landfill site is one of the oldest in North America, dated approximately 700 thousand years. The dire wolf and several other Pleistocene mammal fossils can be seen at the Fossil Discovery Center of Madera County. http://maderamammoths.org/

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Amethyst

Photo by Jim Bryan
From the private collection of Mike & Chris Whittier of Rocks in a Hard Place

Amethyst (SiO2) is a semi-precious variety of Quartz. It is very popular as a specimen and in jewelry. It is even claimed to have mystic properties. Although not rare, its desirability keeps its value high.
This specimen comes from Brazil.

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Camel

Photo and information by Larry Martin
Camel photographer unknown
Courtesy of the Fossil Discovery Center Of Madera County


Western Camel

Camelops hesternus

The Western camel was one of two species of the camel family that existed at Fairmead. Western camels were large herbivores, standing up to 14 feet in height. The camel family evolved in North America during the Middle Eocene Epoch, 40-45 million years ago. Many different species of camels were present in North America during the various geologic ages. Eight different species were found in California alone. Camels migrated to Asia 4-5 million years ago across the Bering land bridge. All camel species in North America were extinct by 11,000 years ago. Distant relatives of these ancient camels still exist in South America today as llamas, vicunas, alpacas, and guanacos.

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Geode


Photo by Jim Bryan
From the private collection of Mike & Chris Whittier of Rocks in a Hard Place.

Geodes are nodules that have a hollow center. They are usually formed by silicate material lining a pocket, or vug, in a rock formation. The inside is often lined with crystals, generally a variety of Quartz or Calcite.

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Peccary