Saratov
An L 4 Olivine-hypersthene chondrite.
Fell 1918, September 5,
Near Donguz, Penza, Russia Saratov is a famous and well-documented meteorite. It had a spectacular fall with fireball and explosions, and it has become known for its exceptionally large and plentiful chondrules – with some inclusions measuring almost one cm in diameter!
It is also a fragile meteorite. Saratov has a loose and crumbly consistency, so that it can hardly be sawed into stable thin slices. And depending upon who produces slices of the meteorite, it can degrade and show rust halos that form around the chondrules within a short time after cutting.
But what a gorgeous meteorite!
Photo by New England Meteoritical Services. www.meteorlab.com
Here's a photo of the edge of the above sample:
Photo by New England Meteoritical Services. www.meteorlab.com
As you can see, wonderful chondrules, almost falling like small grapes. But what a wine. And an education.
Stone Meteorites and Their Parent Bodies
- Meteorites are generally accepted to be samples of asteroids, thus the physical properties of meteorites are likely to be indicative of those of asteroids.
- Most stone meteorites (the ordinary and carbonaceous chondrites) are dominated by distinct subunits – matrix, chondrules and inclusions.
- The chondrules and inclusions are large (~mm size) and strong, while the matrix is usually fine-grained and weaker.
And Saratov does not disappoint.
It is not a typical L4 ordinary chondrite. It has a chondrule-rich composition with a friable matrix texture (See below). More importantly, it contains a separate petrographic component - one consisting of highly porous, low-density, fine-grained aggregates, similar to interplanetary dust particles.
This extremely fragile material, which was incorporated on the L chondrite parent asteroid, is usually vaporized as it enters the atmosphere. But, with Saratov, it can be studied.
Analysis
When Saratov is divided up and analyzed, the coarse-grained fractions have significantly more chondrules than the fine-grained fractions.
The matrix particles have angular forms with sharp angles, and there are impact micro-craters on the surfaces of the chondrules. However, no traces of impact melting were found in the matrix material or in the craters.
The principal minerals of Saratov matrix are pyroxene, olivine, sulfides, metal. The interesting fact is the differentiation of matrix composition is dependent on grain size: pyroxene predominates in the coarse-grained fractions (about 70% of meteorite particles), olivine predominates in the fine-grained material (not less than 60% ) .
Lithic fragments (See below) are present in Saratov meteorite. These fragments are highly porous, not dense, and have a globular structure of small silicate grains. The fragments also have a low metal- and troilite-content, and are composed of plagioclase. All of the fragments, which are low-calcium pyroxene and kamacite, are different from that of the meteorite in general.
However, the features of the fragments - porosity, density, mineralogy and structure - are most similar to those of interplanetary dust, and, to a lesser extent, also similar to lunar breccias and agglutinates (See below).
This infers a similar mechanism of agglomeration (See below) from fine mineral dust by means of electrostatic sticking, followed by formation of friable aggregates (See below).
The highly porous fragments were buried and preserved during agglomeration of the chondrite matter. Their survival inside the parent body testifies to the formation of the chondrites on the surface of, or at small depth, in the parent body.
Later, shock metamorphism induced partial structural and composition transformation in the whole meteorite.
The presence of these unique highly porous fragments in Saratov can be important evidence of:
- Regolith formation on the surface of the meteorite parent body and/or
- Existence of friable bodies in space.
These bodies cannot penetrate the atmosphere of the Earth. The famous Tunguska phenomenon could be connected with such cosmic matter.
Side Note
One analysis of Saratov used the NASA Ames Vertical Gun. A slice of Saratov was struck by an ~5 km/sec Aluminum projectile, a speed comparable to the mean collision velocity in the main asteroid belt. A conclusion of the test was that Saratov contained very little matrix
Here's another photo of Saratov. A close-up of its surface:
Photo by New England Meteoritical Services. www.meteorlab.com
As you can see, Saratov is a mass of chondrules tightly grouped and consolidated into a meteorite.
Terms
As we have seen with other meteorites, Saratov is a wonderful teaching example. Here's some of the terms used to describe the meteorite.
Definition of Agglomeration
- n. The act or process of collecting in a mass; a heaping together.
Image from http://www.lexic.us/definition-of/agglomeration
Definition of Agglutinate (s)
- a. United as if by glue.
Here's a Lunar sample of a dull, dark grey agglutinate – highly magnified of course:
From http://minerva.union.edu/hollochk/c_petrology/moon_rocks/lunar_images/SD-MS-52.jpg
Definition of Friable
- a. Easily crumbled, pulverized, or reduced to powder.
Picture from http://www.lexic.us/definition-of/friable
Definition of (friable) Aggregate
- n. The whole amount.
Picture from http://www.lexic.us/definition-of/friable_aggregates
So, a friable aggregate is an easily crumbled whole....
Definition of Lithic
1. a. Of or pertaining to stone; as, lithic architecture.
Picture from http://www.lexic.us/definition-of/lithic_fragments
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