the cone fracture principle(1)

8/12/2019 The Cone Fracture Principle(1)

1/14

THE CONE FR CTUREM NUF CTURE OFBy Don E

An understanding of the correlation of the cone

Ancient man took advantage of the nature of

The cone of force associated with lithic tool

le about one of the sides containing the right

of force is not pointed like a m athemati-

PRINCIPLE N D THELlTHlC M TERI LSrabtree

In determinative mineralogy the word conch oi-da1 -from the Greek wo rd shell s used in co n-junction with fracture to indicate the shell-likeform produced on the surface of vitreous isotropicminerals by fracture. Conchoidal fracture leaves anegative concave scar similar to the interior of abivalve shell on the surface of the artifact henegative cone scar. The detached flake representsthe positive side of the shell-like form and will beconvex like the exterior of a bivalve shell hepositive cone scar. The hinge part of this hypothet-ical shell is the cone truncation or the part receiv-ing the force to induce fracture.Because man the toolmaker was using the

cone principle to detach flakes, he had to choosematerials which would be receptive to cone forma-tion by force. When vitreous material is worked,cones of force will shear or will be formed deeperin the mass with approximately the same amountof force applied to granular material. Granular ma-terial appears to dissipate the cone-forming forcemore readily than glassy material. This is becausegranular material lacks the elastic qualities of vitre-ous material. Elasticity is the quality or conditionof bein g elastic or springy hat inherent pro p-erty in materials which allows them to recover theiroriginal form or volume after any external pressureor force has been dissipated. Elasticity is the ut-most extent or limit to which elastic materials canbe extended or compressed without fracturing. Vi-treous isotropic materials used in the lithic indus-tries are almost perfectly elastic. Degrees of elas-ticity are dependent on the homogeneity of themicro -crystalline structure he more vitreous,the more elastic the material. For example, obsidi-an and other glassy materials are considerablymore elastic and springy than quartzite; and na-tural flint is more inflexible than thermally treatedflint which has been made more vitreous by arti-ficial means.

The term cone of force (Fig. 1 B) is used in thistext to denote the visible part of the cone withoutimplying the type of applied force. Many texts re-fer to the cone of force as the bulb of percu s-sion , thereby d e n o t i n ~ hat the cone part, orflake, was detached by the percussion technique.There are other techniques of flake detachment,and cones may be formed by pressure and indirect


2/14

to use the term bu lb of force or cone of

ither bulb of percussion or bu lb of

one truncation (Fig. 1B-C) occurs at the apex

The yield of the percussion tool and the portion

lock-on -block, cause the cone truncation

blade from the core, the

When lithic material is subjected to stress, the

and causing cone to be formed. When

the applied force surpasses the elastic limit of thematerial, fracture results (Fig. 1D-E). Fracturestarts at the apex or vertex of the cone and termi-nates at that basal margin. Therefore, the directionof applied force is different from the fracture angleof the cone. One must bear in mind that a flakescar which is derived from the fracture angle of thecone results from force which is applied at otherrhan a right angle or perpendicular to the centralaxis of the cone and is tangential to the directionof fracture.A common inverted funnel (Fig. IF) can beused to illustrate the cone principle. The stem ofthe funnel represents the direction in which forceis applied. The sides of the funnel represent thefracture angle of the cone an d the apex of the cone(platform) is the part of the funnel where the neckor stem joins the flared part of the funnel. The fun-nel can be overlaid on the flake or cone scar andihe stem of the funnel will indicate the direction atwhich force was applied. The flare of the funnel'ssides may not be quite the same as the angle ofthe cone, but the stem can indicate the approxi-mate direction of force. One can make an isoscelestriangle from cardboard or a piece of plastic andaffix the apex of the triangle to a small dowel to beused as an indicator to determine the direction offorce (Fig. 1 G . This small tool is a useful devicefor showing the direction of applied force to re-move a flake or blade from an artifact or core (Fig.2). The gauge helps in discriminating between na-

ture facts and artifacts. The gauge also helps todetermine the angle at which force was appliedand when the angle or angles represented by flakeor blade scars are known, one may then recon-struct the action that was involved in the formingof the core or implement.There are exceptions to the rule of using thefracture angle of the cone to determine the direc-tion of force, e.g. (1) splitting or shearing of thecone by opposing bi-polar forces or due to inertiaand (2) cone collapse due to excessive compres-sive force.The type of applied force determines the for-mation or spacing of the compression (stress) ringsaround the circumference of the cone. The com-pression rings undulate in different degrees of in-tensity, comparable to water or sound waves. Forexample, blows of high velocity delivered with ahard hammerstone cause the stress wave intervalto be closely spaced, while a slow blow with asoft percussor will cause the wave interval to be

widely spaced. Soft hammer wave intervals ap-


3/14

proach those produced by pressure. The wavesseem to be quite regular pulsations that start at theapex of the cone and continue to the terminationof the cone fracture. Normally, the pressure tech-nique produces slight or subdued compressionrings.Prehistoric stone tools are generally made byapplying sufficient force to lithic material to induceadequate stress to form a cone which expands

from its apex and detaches a portion of the stone.The detached piece is a f lake but is also a conepart. Some flakes are half cones, others are quar-ter cones or parts of cones. Full cones result fromforce directed in from the margin at 90 to theplane surface. Half cones result when force is dir-ected at 90 on a right angle margin. Quartercones are formed by the force being directed ver-tical to the corner of a rectangular bloc k Fig. 3A).The detached material can assume a variety offorms; all will have a complete or portion of thecone of force. These parts removed from near themargins are called flakes. Some flakes are spe-cially designed, elongated flakes called blades.Flakes resulting from early stages of artifact manu-facturing often appear to be aberrant and withoutdesign, where in reality they are due to the amor-phous nature of the rough material or to individualplatform preparation.The flake form is usually directly related to theexterior surface 6f the material and the fractureangle of the cone of force. The shear plane is the

same as the fracture angle of the cone and is tan-gential to the direction of applied force. Therefore,the force is applied at an angle to the fractureplane of the proposed flake or flake scar. Nor-mally, the flake form will correspond to the exteriorsurface. This rule is not applicable to very thickflakes where the thickness is greater than the sur-face conformation, shape, structure or design. Theform of the cone part can be designed by first pre-paring the surface. A plane surface will allow theflake to expand from the point of applied force, re-sulting in a typical conchoidal or shell-like conepart. A predesigned ridge or ridges will restrict theexpansion of the flake and its detachment will re-sult in a cone part called a blade. Another exampleof flake form control is the use of ridges to preventthe expansion of the flake. When the worker alignspressing forces with a pre-established ridge andremoves a series of elongated cone parts, it willresult in what is known as parallel flaking.

The following interpretation of the cone prin-ciple is based on the study and results of numer-

ous experiments in replicating aboriginal flakingtechniques. Circumstances have not permittedcontrolled laboratory investigation of exact anglesrelated to force, inertia, mass, motion, veiocitiesand properties of. materials, but the experimentshave been verif ied by duplicating and comparingboth cone and cone scars on isotropic materialsformed by both man and nature. Slight variationsof the angle of force do occur, but when all con-ditions, elements and circumstances are the samethe fracture angle will be the same Fig. 38 ).

Cone parts in the forms of flakes or bladeshave almost universal distribution, while intention-ally made complete or full cones have limited oc-currences. But even though the aboriginal flint-knapper did not use this technique for forming arti-facts, he did make full cones when he was perfor-ating stone. I have noted use of the full cone re-moval technique in the State of Colima, Mexico,and Jacque s Tixier persona l commu nication) hasfound examples of the use of this technique to p2r-forate beads in Egypt during the Chalcolithic. TheEgyptian bead making technique exhibited slighttechnological differences from the blexican methodof perforations. In Egypt beads were made byusing a very small tube drill to first drill half waythrough flakes of vari-colored chalcedony, andthen the balance of the material was punched outby removing a full cone with a cylindrical trunca-tion Fig. 3C). Surplus material was then removedfrom around the perforation, making the bead dis-coidal. In Colima, Mexico, perforations of obsidianwere made by removing minute, complete conesfrom the margins of eraillure flakes Fig. 3D).

Eraillure flakes are specialized flakes. They aregenerally circular concavo-convex and are formedbetween the flake and the core by direct percus-sion. The eraillure flake either falls free or remainspartly attached to the core. The dorsal side of theflake is usually without compression rings and theconvex side has a good reflecting surface. Thepiece is made regular and the sharp edges re-moved around the circumference by pressure flak-ing. Perforations in the discoidal eraillure flake aremade by using a pointed dril l to dril l an indenta-tion approximately half way through the disc. If theflake is to have one perforation in the center, thehole is drilled in the middle on the concave side.If two holes are to be rnade, they are drilled oppo-site each other slightly in from the margins. Afterthe drilling has established an indentation, a sharppunch of very resistant material is seated in the in-dentation and the punch struck, removing a conefrom the opposite face to complete the perforation.


4/14

Experimentally, I have perforated lithic material

or vertical, otherwise the cone will be acute,

5 O to the plane surface. The thickness

Another full cone experiment is accomplished

A pea-sized

back. When it is released it strikes the small peb-ble and the impact perforates the material by re-moving a cone. Shattering is common until the cor-rect velocity is achieved.Another full cone experiment involves selectinga piece of lithic material with a natural flat surfaceor by making a flat surface to receive the impact,and then imbed the stone in wet sand. The planesurface is placed upward and then struck verticallywith a hard percussor. The size and velocity of thepercussor must correspond with the size and in-ertia of the objective piece. This method will per-forate the piece by removing a full cone, but untilone becomes proficient at the technique, he willhave more failures than successes.SinCe cones and cone parts are the result offorce applied to isotropic materials, they may bethe result of either natural or human force appliedby pressure or, more commonly, by percussion.

Natural forces result from a wide variety of causesand may, under the right conditions, form conesand cone scars on stone which will be similar tothose made by man. However, natural scars onlithic material are generally random and do not re-flect the preconception, planned order, rhythmsand muscular motor habits necessary for man toproduce his tools. Close examination and analysisof the scar character and the fracture angle ofthe cone of force will indicate the direction of ap-plied force and may reveal that they are a naturalrandom imitation rather than preconceived and cal-culated human endeavors. Flakes intentionally de-tached by man have sharp edges and generallyleave sharp edges on the objective piece prior toperforming functional chores. Conversely, naturalfractures produce flakes and cores with abradededges due to indiscriminate pressure and percus-sion. Utilized tools may exhibit dulled edges butgenerally have a distinctive wear pattern.

Should a row of flake scars removed in se-quence be present along a margin indicating con-sistent directions of force applied with the sameintensity, the probability is that this is a product ofman's endeavor rather than a result of natural ac-tion. Man-made flake scars will generally bearthe same amount of erosion. Erosion differentialwill indicate that the flakes were removed at dif-ferent times. Differences in erosion will be morecharacteristic of nature than of man's remodifica-tion of an artifact. However, occasionally one willfind evidence of differences in erosion of patinaon a man-made implement. This is generally an ar-tifact which has become dulled or broken and then


5/14

rked. However, the second stages of re-

Natural cones of force are common in lithic de-

ceable in vitreous stone with isotropic proper-han in granular rocks. One pebb le striking an-

*m ay cleave the object at thei t is possible for the cone of

The determining of the geological occurrencevitreous material minerals) is important before

i.e.siliceous sandstones q~ lar tzite , not

etions in sedimen tary rocks flint in lime-

ders in alluvium. Quite naturally, vitreous mineralsin the form of alluvium or occurring naturally whichare rolled and bruised prior to redeposition arerounded since the corners or protuberances areless resistant to battering. During the movement,the striking of one piece of stone against the otherwill detach flakes. Rounded or ovoid materials aremore resistant to fracture than angular ones. Theinvestigator can expect to find somewhat differentstyles of natural fiake and flake scars in depositsof materials depending on their geological occur-rence. Angular material deposits can fracture intocore-l ike oieces with n occasional scar at the8corner, or corners, which will resemble a bladecore. Thin tabular pieces will have an edge thatwill appear to be a burin core. The right anglemargins of the tabular or angular pieces will haverandom conchoidal scars of assorted sizes, theedges being somewhat crushed and abraded.Flakes which match the flake or blade scars shouldbe in association. Starch fracturing is not uncom-mon in natural deposits of obsidian and siliceousvitreous minerals and causes some interestingpseudo artifacts to be formed, many resemblingblade cores and blades. However, with starch frac-tured material there is no bulb of force, but thereare occasional rings of compression.

The natural tumbling action which forms inter-secting cones on vitreous lithic materials is similarto the pecking technique used by man to reduceand shape implements. The process is calledpecking and is a percussion technique of repeat-edly striking the object to cause cones of force tointersect one another, thereby freeing the materialbetween the fracture planes. A percussor of vitre-ous material is desirable because after continueduse it will develop slightly projecting positivecones. These positive cones on the percussor willin turn form multiple cones on the material beingreduced by pecking from a single blow. A percus-sor of the proper material will remove a quantity ofmaterial from the objective piece in a short time.Experiment has shown that when the worker usesa percussor of the proper weight and material, hecan groove a basalt or granite maul in less thancne hour. When pecking is used to reduce non-vi-treous material the cones are often crushed, newones made and then crushed causing a rapid re-duction of the material. Crushing occurs becausecones intersect and collapse so that chunks of ma-terial fall away rapidly. The percussion cone tech-nique was used to form and groove axes andmauls, inscribe petroglyphs, make bowls and mor-tars, to make heads for war clubs, shape masonryand make ornamental carvings.


6/14

The fractu re angle of the cone and the inter-

-13). Pressure re touch used in beve ling andbi-di-

principal but pressure is applied in two direc-tool m ay be held at differ-

de termination. T he fracture angle of the

F-G).When rounded, spheroid material is fractured

hether by nature or man t must receive

9 o the

the cone of force leaving no bulb of force or apoorly defined one with closely spaced compres-sion rings. When the force is excessive and thecones of force collapse, the debris is angular andthe flakes are sub-triangulate in section, similar toan orange segment. The force waves will be close-ly spaced with expanding shatter line originating atthe point of applied force. When the cone issheared there will be no evidence of the bulb offorce, the fracture plane is quite flat and the com-pression rings are also closely spaced.PPLYING THE CONE PRINCIPLETO FUNCTION L FL KE SC RS

A careful study of the use flake scars on stonetools can sometimes determine their functionalperformance and also indicate the manner of hold-ing. Past studies of such scars have placed em-phasis on the plane of fracture, but have not con-sidered the angle of applied force which is, inturn, governed by the angle at which the artifact isheld when performing a spec ific function. For thepurpose of enc oura ging further and m ore detailedstudy of these scars, I would like to postulate apotential use of applying the technique of flint.knapping to more clearly define these functionalscars. It is conceivable, and I believe p ossible, thatthe principle of the cone as applied to intentionalfracture in tool making could be useful in diagnos-ing functional flake scars (Fig. 6).Two angles of force must be interpreted andthese angles are indicated by the type, length andtermination of the use flake. Applying the principleof the angle of the cone to the n egative flak e scarcould very well determine the angle at which theartifact was held. The use flakes may be related tothe fracture angle of the cone and direction of ap-plied force and, in turn, used to show the mannerin which the tool was held. When the tool was usedas a chopping implement by impact or percussion,the fracture angle of the use flakes and cone re-main relatively constant (Fig. 6). When the tool ishand held and pressed, rather than projected, twoangles of force must be considered. It is possiblethat a single direction of pressure force could beapplied until the cut is terminated. If the cut doesnot terminate, two directions of pressure are usedto complete the cut. Should an involuntary useflake be detached, it will correspond to the propor-tion of the forces, changing the fracture angle ofthe normal percussion cone of force. When a flake,or blade, is used as a knife for cuttina flesh, hide.sinew or materials with minor resistance it can be

Natural fracturing by violent battering shears held at the proximal end between the thumb and34


7/14


8/14

CKNOWLEDGMENTS torial assistance William Statham and Dale Pettyfor he lp in the preparation of illustrations my wifeam grateful to the National Science Founds- Evelyn for typing the draft and encouraging mealong the way and Wendy Kerbs for typing the finalcopy of the paper.also wish to acknowledge the assistance of Idaho State universityH. Swanson Jr. and Richard Gould for edi- useumPocatello Idaho

Crabtree, Don E.

1972 The Cone fracture principle and the Manufacture of lithic Materials.

En: Tebiwa. The Idaho State University Museum. Vol. 15 No. 2


9/14

DIRECTION OF DIRECTIONFORCE OF FORCE/O R C O N EFRACTURE

CONETRUNCATIONFR AC TU R EANGLE \

1. A the mathematical cone; B a full cone of force showing its principal features; C a flake showingits principal features; D and E the stages for producing a full cone when lithic material is sub-jected to stress; F a common inverted funnel; G a small gauge which can help indicate thedirection of applied force.


10/14

2. Some application s ot the gauge to different shaped specimens to determine the direction of applied force.


11/14

E R A I L L U R E CR O S S S E C T I O NW I T H S O L ID D R I L L HOLES

P L A N E

CONETR U N C ATION

SURFAC/ PERFORATION

3 A examples of where particular cone parts are formed in a rectangular block when force is ap-plied to particular areas; B the formation of similar cones occurs when all elements are the sameexcept the direction of applied force; C the Egyptian method for the perforation of beads; D theMexican method for perforating eraillure flakes; E-G the stages in the perforation of a tabularsection the preparation of a plane surface on a cob ble the formation of a full cone by using ahard percussor and finally the removal of t h perforated tabular section.


12/14

4 The direction of applied force and fracture angles when only single direction force is used

40


13/14

. 5. The ap plication of bi-direc tiona l force use d in the pressure technique A the application ofdownward and outward pressures to produce a blade; B the application of inward and outwardpressure to flake a projectile point; C the di ffe ren t angles at wh ich a pressure tool may be heidduring pressure flaking.


14/14

6. The cone fracture principle as applied to intentional fractures can be useful in diagnosing functional flake scars.

the cone fracture principle(1)

Documents