Herkimer Diamonds

These are not true diamonds, but they have their own beauty. Herkimer “Diamonds” are naturally double-terminated (also called “double point) quartz crystals that can have amazing clarity (truly crystal clear). Each crystal is a six-sided prism terminated at both ends by a rhombohedron: thereby making 18 crystal faces (facets). When the terminations are equally developed, the appearance is that of a hexagonal dipyramid. 

Herkimer “Diamonds” are unlike diamonds in that the former are natural and do not require cutting and smoothing by humans. Herkimer “Diamonds” have a hardness of 7 on the Mohs Scale (note: all quartz has a hardness of 7); thus they are not as hard as true diamonds, which have a hardness of 10.

Herkimer “Diamonds” are found at and near Herkimer, Herkimer County, New York, about a 4.5- hour drive west from New York City. These crystals occur in the very fine-grained, gray-colored Little Falls Dolostone of Cambrian age (500 million years old). Dolostone is a combination of dolomite and limestone, and dolostone fizzes weakly in a 10% solution of hydrochloric acid.

The Herkimer “Diamond” crystals always occur in vugs (cavities, like those associated with geodes) within the dolostone, and the precipitation of these crystals probably took place during the Carboniferous age, about 300 million years ago. The Herkimer “Diamond” crystals need air space. Without the “air space,” they cannot form doubly terminated crystals. They do not adhere to the dolostone. They can adhere, however, to each other, but only at the end points of the crystals. Thus, they weather out of the outcrop as individual crystals. Their value depends on the their size and how clear (translucent) they are. Some of the crystals have inclusions (small fragments of impurities), which are most commonly pieces of black hydrocarbon material.

Shown below, is a tiny Herkimer “Diamond” quartz crystal (5.5 mm long and 2.5 mm wide) still inside a tiny vug in the Little Falls Dolostone. 

Below, a larger Herkimer “Diamond” crystal (22 mm long and 9 mm wide) is shown. This crystal is not perfectly clear. It has some incipient milky quartz cloudiness, which comes from microscopic inclusions of fluids stemming from when the crystal grew. This specimen also has some black hydrocarbon inclusions.

If you are ever in the vicinity of Herkimer County, you might want to stop and do your own collecting (for a fee). It is not every day one finds doubly terminated quartz crystals that are so perfectly clear.

REMARKABLE SLUMP-FOLDED BEDS

This post concerns an “eye-popping” section of extremely slump-folded sandstone beds within the Chatsworth Formation, in the Simi Hills of Ventura County, southern California. You have to see the actual beds, or see a picture of them, in order to believe it.

These slump-folds are of Late Cretaceous age (late Campanian/early Maastrichtian age, about 70 million years old). They are located on protected land.

Three images of these slump beds are shown below (a person provides the scale): the first two are essentially the same view, but the second of these two was taken under different lighting. The third image is of the same channelized flow but a several meters westward, near the lowermost part of the slump feature.

The folded/crumpled beds consist of numerous wedge-outs of sand-rich deposits (with a sandstone to mudstone ratio of 12:1). These beds filled a braided-channel, turbidite deposit in a deep-sea-fan system of a submarine middle-fan environment (see references below for all the gory details). Turbidites are deposits of sediment-gravity flows which include turbidity currents, fluidized sediment flow, grain flow, and debris-flow mechanisms. The beds were originally in a semi-liquid state, unstable, and slid down a slope.

For more details, see the following references:

Link, M.H. 1981. Sand-rich turbidite facies of the Upper Cretaceous Chatsworth Formation, Simi Hills, California. Pp. 63–70, in Link, M.H., R.L. Squires, and I.P. Colburn, (eds). Simi Hills Cretaceous turbidites, southern California. Pacific Section, Society of Economic Paleontology and Mineralogy [Guidebook]. Los Angeles, California. 134 pp.

Note:  This slump fold was illustrated also on the cover of AAPG, v. 67, no. 3, 1983.

Link, M.H., I.P. Colburn, and R.L. Squires. 1984. Slope and deep-sea fan facies and paleogeography of Upper Cretaceous Chatsworth Formation, Simi Hills, California. The American Association of Petroleum Geologists, v. 68 (no. 7):850-873, 22 figs., 4 tables. Note: See Fig. 12D for a picture of the slump fold illustrated in this present blog post. 

How And When Did Monkeys Get To South America?

Monkeys live today in the Old World (Africa and Asia) and in the New World (South America, Central America, and southern Mexico). The consensus has been that they originated in Africa, but it is not known with certainty how they managed to get to South America. You might think that the answer is they that they simply walked from Africa to South America, but the answer is not that straightforward. 

Here are the paleontologic facts: 

The earliest known fossils of monkeys are found in Africa (Egypt) and in South America (Bolivia and in the Amazon region of Peru). They are all about the same geologic age: latest Eocene/early Oligocene (about 33-35 million years ago). The problem is that there was 1,400 km of open ocean between Africa and South America at that time (and previously for a long time—millions of years earlier, during Cretaceous time).

So, that nagging question is: “how did monkeys get from Africa to South America.” The usual answer, which that has been around since the 1960s and is still in vogue today, is that African monkeys floated on clumps of forest vegetation (e.g., modestly large forested islets) that floated downriver and eventually ended up in the ocean. These clumps then drifted across the Atlantic Ocean to South America during late Eocene/early Oligocene time. The shortest distance would have would been 1,400 km, and the drifting is estimated to have taken at least 60 days. Then monkeys then would have had to transverse overland a long distance, from the eastern shores of South America, in order to reach the inland jungles of Bolivia. This widely believed “floating-vegetation theory” is commonly referred to as the “accidental transoceanic dispersal” theory. 

Another theory is that the earliest monkeys reached South America via southern North America during late Eocene time. This theory, as well as the one discussed above, are questionably indicated on the following known paleogeographic map that shows the position of South America, relative to North America and Africa during the late Eocene. The few scientists who advocate this second theory of a dispersal route via North America have proposed, furthermore, that monkeys originated even earlier that late Eocene time. For example, in Wyoming, a sparse record of early Eocene fossils that resemble marmosets (= New World monkeys) is known.

 

While you contemplate the unsolved mystery of the ancient geographic dispersal of monkeys, it is useful to give you some background biologic information to consider. Monkey are primates. Primates include the prosmians (lemurs, bush babies, lories, pottos, and tarsiers) and also the anthropoids (monkeys, gibbons, apes, and humans). Old World monkeys consist of several families, and these are referred to as the catarrhines. They are characterized by having nostrils separated by only a thin partition, and they also have jaws with two premolars. Two examples of catarrhines are the macque monkey and baboons. Old World monkeys do not have prehensile tails. Old World monkeys include both arboreal (live in trees) and ground-dwellers.

An example of a modern-day catarrhine monkey (from Japan) is shown above. Photo credit: Wikipedia, 2021.

The New World (South America, Central America, and southern Mexico) monkeys are referred to as the platyrrhines. They are characterized by having nostrils that are quite separate, and they also have jaws with three premolars. Two examples of platyrrhines are shown here: cebids and marmussets New World monkeys have a grasping prehensile tails. New World monkeys are only arboreal.

An example of a modern-day platyrrhine monkey (cebid) from Costa Rica. Photo credit: Wikipedia, 2021.

A second example of another modern-day platyrrhine monkey (marmoset). Photo credit: Wikipedia, 2021.

A relatively recently published comparative study of mitochondrial genes of primates has been interpreted as agreeing with the fossil data showing that platyrrhines split from catarrhines at around 35 million years ago. The authors of the mitochrondrial study also advocated the “floating on vegetation” theory (see discussion above).

USEFUL REFERENCE;

For an excellent article concerning evolution of mammals in South America, I highly recommend: https://dcpaleo.org/south-americna-fossil-mammals/

TERROR BIRDS

The generalized term “terror birds” is the focus of this post. It refers to a group of extinct similar looking birds that could be up to 8 or 10 feet tall and weighing 400 pounds. There were several genera/species, and they make up an extinct group of carnivorous flightless birds, referred to as the phorusrhacids. They were the largest apex predators to live in South America during the Cenozoic Era.

One example of this group is genus Phorusrhacos [pronounced For-us-Rah-koss], of middle Miocene age, about 14 million years ago, from Santa Cruz, southern Argentina. Although it superficially resembles an ostrich, it is not one. The skull of Phorusrhacos is very different. Phorusrhacos was 8 feet tall and weight 300 pounds or more. A model of this genus is shown below. 

The geologic time range of “terror birds” is most of the Cenozoic, from late early Paleocene, late Danian Stage [=62 million years], through the early Pleistocene [=1.8 million years]; an interval of approximately 60 million years. Why did they go extinct? Most likely, it was because of changing habitat (related to changing climate during the Pleistocene Ice Age). Also the Panamanian Land Bridge emerged during the Pleistocene, and South America became connected to North America, and large predatory cats and dogs migrated southward into South America for the first time.

It is interesting to mention that the geologically youngest “terror bird” (Titanis walleri = 8 feet tall and 300 pounds), of early Pliocene to early Pleistocene, lived in Texas and Florida. This shows that at least a “terror birds” migrated northward into North America, but their presence there did not last long.

The geologic history of birds, in general, is a complex subject. They originated during the “time of dinosaurs” during the Jurassic Period, but their diversity increased significantly during Cenozoic time. A very generalized cartoon showing the major different groups of Cenozoic birds is shown below. The “story” of bird evolution is still unfolding.  

I encourage you to “Google” the words “terror birds” or Phorusrhacos. There are MANY online colorful renditions of what this animal and its relatives looked like. 

Wild Turkeys Once Lived in Southern California

 This post is appropriately “published” just prior to Thanksgiving Day, 2021 and gives a nod to the turkey, a bird native to North America. 

The earliest known fossils of turkeys are of early Miocene age (23 million years old). They are from near the small town of Bell, northern Florida in northern Gilchrist County, approximately 30 miles northwest of Gainesville. These fossils belong to the extinct genus Rhegminornis, which was about half the size of the modern genus Meleagris, whose type species is M. galiopavo (also known as the wild turkey). The latter is the largest gallinaceous bird (refers to its order in the classification system of birds) in the New World. It is 3-4 feet tall, 10-40 pounds in weight, and has a wingspan up to 6 feet. These turkeys are very social animals, yet territorial.

Today, M. galiopavo lives in the forests of midwestern and eastern United States and into southeastern Canada. I can verify a Gulf Coast occurrence because I saw a wild turkey in southern Alabama, while I was on a fossil-collecting trip (gastropods and bivalves) many years ago. I can also confirm that this species can fly. The one I saw flew high into a tree top. This wild species is the ancestor of the domestic turkey.

A second living species, M. ocellata, lives in the forests of the Yucatán Peninsula, Mexico.

Another species of Meleagris is the extinct Meleagris californica, which lived in southern California during the Pleistocene Ice Age. Bones of this species represent the second most common fossil found in the Rancho La Brea Tar Pits. The most common fossil is the Golden Eagle. Meleagris californica went extinct about 10,000 years ago.

For more detailed information, I highly recommend that you Google rexmachinablog.com for its excellent blog on “The Wild Turkey: the evolution and history of an American icon.”

If you are interested in detailed information about the Rancho La Brea turkeys, see the following pdf (downloadable, for free):

Bockénski, Z.M. and K.E. Campbell, Jr. 2006. The extinct California turkey, Meleagris californica, from Rancho La Brea: comparative osteology and systematics. Contributions in Science, number 509, 92 pp. Natural History Musem of Los Angeles County, California.

The Silica Tetrahedron

The molecular structure of silica tetrahedron (SiO₄) is the basic building block of the silicate minerals, which make up the vast majority of the minerals in the Earth’s crust.

The silica tetrahedron is a combination of one silicon and four oxygen atoms that form a four-sided pyramid shape, with the silicon atom in the center and an oxygen at each corner of the pyramid.

This low-tech "marshmallow model"shows the basic design of the silicon tetrahedron.

In a more explicit model of a silica tetrahedron (see below), the element silicon is a cation with a charge of +4. Each oxygen atom is an anion, with a -2 charge; thus four oxygen atoms make a -8 charge. The combination of +4 and -8 makes -4. The silicon tetrahedron molecule has therefore has a net -4 charge, which means it readily combines with other elements besides oxygen in order to balance out the additional -4 negative charge and form a net-zero charge (i.e., nature abhors a molecule with a net negative charge; just like nature “abhors a vacuum”).

There are six main configurations (e.g., rings, chains, frameworks etc.) of linkage among silicon tetrahedra. There are many internet sites that show beautiful reconstructions of these configurations, some of which are quite complicated. One of the most useful sites is: <openeduationalberta.ca/practicalgeology/chapter 3>  You will have to access it yourself because Google no longer allows external links within blogs.

The mineral quartz (SiO₂), which is the most abundant mineral in the Earth’s crust is an  example of the framework configuration known as the tectosilicates. In quartz, in order to neutralize the ionic charge difference, the four oxygen atoms of the silica tetrahedron are “shared” by adjacent silica tetrahedra. Each corner of the pyramidal tetrahedron is bonded to another tetrahedra (with an oxygen shared at each corner of each). As a result, the ratio of silica to oxygen atoms is 1:2, and the atomic charge is neutral (zero). 

A cluster of clear quartz crystals (6.5 cm wide, 6 cm high).

A single crystal of clear quartz (2.4 cm wide, 5.7 cm high).

One of the simplest silicate minerals is olivine, which is made up a single tetrahedron bonded to divalent iron (+2) and/or magnesium (+2), thereby creating Fe₂SiO4 or Mg₂SiO4, or some combination of the two (Fe, Mg)₂SiO4. The combination can occur because both iron and magnesium are divalent (+2) [thus they balance the charge of the silica tetrahedron] and their atomic sizes are similar; thus they can substitute for one another.

The above image is a cluster of tiny olivine crystals (hand specimen 3.6 cm wide, 2.7 cm high).

Terminology Hints

The words silicon and silica, etc., get used a lot in our modern vocabulary. The following list might be of some help to you in understanding these similar terms:

silicon (Si) = the 14^th element on the “Periodic Table of The Elements.”

silica = a solid material made out of SiO₂ (but not necessarily a mineral; e.g., opal---see my previous post on chalcedony).

silica tetrahedron = a combination of one silicon atom and four oxygen atoms that form a tetrahedron (= a four-sided pyramidal shape).

silicate = a mineral that contains a silica tetrahedron or many silica tetrahedra. 

silicone = a flexible synthethic material made up of Si-O chains with added organic molecules.

SMITHSONITE: the blue-green variety

Smithsonite was named in honor of James Smith, founder of the Smithsonian Institution.

This mineral belongs to the carbonate group and consists of zinc carbonate ZnCO3. It effervesces in hydrochloric acid. Its streak is white, and it has silky luster, its specific gravity is 4.4–4.5, its hardness is 4.5. Its crystals belong to the trigonal system, but they are rare. Smithsonite commonly occurs in either a globular (botryoidal) or in a massive (granular) form. 

It has a wide range of colors because of chemical impurities (listed here in brackets): white to gray [no impurities]; blue, blue-green, to apple green [copper]; yellow [cadmium]; pink to purple [cobalt]; and brown to red [iron].

It often forms as a secondary mineral in the upper oxidation zone of zinc-ore deposits within metamorphic rock complexes. It is found in Greece, Spain, Africa, and the USA (one famous example is at the Kelly Mine in New Mexico).

The two images shown above are of the botryoidal form of an encrustation of smithsonite (38 mm length an 9 mm in height) from the Kelly Mine at Magadalena, Socorro County, central New Mexico.