ON MOTION FOR REHEARING
REAVLEY, Justice.The judgment of the Court of Civil Appeals was affirmed by our judgment on May 25, 1977. The motion for rehearing of Bette Reed, Trustee, is hereby overruled, but the opinion of May 25 is withdrawn and the following opinion delivered in its stead.
The ultimate question in this case is whether a 1950 deed, which reserved to the grantor one-fourth interest “in and to all oil, gas and other minerals on and under the land and premises herein described and conveyed,” reserved one-fourth of the interest in coal and lignite. The trial court rendered a summary judgment in favor of the owner of the granted surface estate, but the Court of Civil Appeals held that the proof did not support a summary judgment and remanded the case for trial. 538 S.W.2d 186. We agree with the Court of Civil Appeals that the summary judgment was unwarranted. We also agree that Acker v. Guinn, 464 S.W.2d 348 (Tex.1971) rules the ultimate issue of the case, but questions raised in the lower courts require that we make certain the effect of Acker v. Guinn before the case proceeds further.
By a deed dated September 30, 1950 W. C. Wylie and wife, Iva Jack Wylie, conveyed 223.385 acres of land in Freestone County to James F. Baker. That deed contained the following reservation:
In addition to the above and foregoing exception there is hereby excepted and reserved to the Grantors herein a one-fourth (V4) undivided interest in and to all oil, gas and other minerals on and under the land and premises herein described and conveyed; and it is hereby expressly agreed and understood that Grantors herein, their heirs and assigns shall have, and they hereby have the right of ingress and egress for the sole and only purpose of mining and operating for oil, gas and all other minerals, on and under said land, and to produce, mine, save and take care of said products, and to take all usual, necessary and convenient means for working, preparing and removing said *171minerals from under and away from said land and premises.
All of the interest conveyed by this deed to James F. Baker is now owned by Bette Reed, Trustee. The controversy is between Wylie and Reed as to whether Wylie retained the ownership of a one-fourth interest in coal and lignite in this land by virtue of the reservation in the 1950 deed as set forth above. Reed initiated this suit seeking a declaratory judgment and other relief.
By summary judgment the trial court declared that Reed is the owner of “all of the coal and lignite that may be mined and removed” from the land “by open pit or strip mining methods.” Reed, the surface owner, was apparently satisfied with that trial court judgment. Wylie, the owner of the mineral interest reserved by the quoted provision, appealed to the Court of Civil Appeals. The Justices of that Court delivered three opinions. The principal opinion addresses only the inadequacy of the summary judgment proof. A concurring opinion states that the surface owner Reed is not entitled to all lignite “that may be mined by open pit methods” but by the rule of Acker v. Guinn is entitled to “only the lignite that must be removed by such methods.” 538 S.W.2d 189. A dissenting opinion states that the trial court’s judgment should be affirmed but reformed to declare that surface owner Reed “is the owner of all of the coal and lignite that must be mined and removed by open pit or strip mining” 538 S.W.2d 190.
Both parties sought writ of error in this Court. Reed contends that the trial court’s summary judgment was correct and should be affirmed. Wylie argues that Acker v. Guinn does not apply to the particular reservation here or to the substance of lignite. Wylie also is critical of the rule announced in Acker v. Guinn and argues that at the proper time, or here if necessary, it should be reexamined.
Wylie is joined by amici curiae briefs in the criticism of Acker v. Guinn. We are told that the mineral owner should expect to get all of the mineral substances beneath the surface of the land and that the law would afford more certainty in these affairs of titles and business if the ownership of the minerals were vested in that owner subject to the usual limitation that he may not make an unreasonable use of the surface in the production or extraction of the minerals. We are inclined to believe that in most of these cases of unnamed minerals which later become very valuable, the subsequent controversy decides which party will be enriched by a substance which took no part in the intention or bargaining of the parties to the instrument of conveyance. Furthermore, we are not convinced that a rule of law which leaves questions of reasonable use of the surface, in each instance where mineral substances at or near the surface are to be produced, will lead to more certainty and less litigation. But whatever the merits or demerits of the holding in Acker v. Guinn, it was established by this Court six years ago, and those persons who have dealt in mineral and land interests during these years have assumed that what we said in that opinion would continue to be the Texas law. They assumed correctly. We reaffirm the holding and the writing in Acker v. Guinn.
The Rule of Acker v. Guinn
(464 S.W.2d 348, Tex.1971)
The question in Acker v. Guinn was whether an interest in iron ore passed to the grantee in a 1941 deed which conveyed “an undivided V2 interest in and to all of the oil, gas and other minerals in and under, and that may be produced from” a tract of land in Cherokee County. The ore deposits in the area varied in thickness from a few inches to three or four feet and ranged in depths from outcropping on the surface to as much as fifty feet below the surface. There was no question but that the ore must be mined by the open pit or strip method. The Supreme Court affirmed a summary judgment in favor of the surface owner.
The Court wrote that a general intent rather than the specific thinking or intent of the parties should be the inquiry *172where the instrument itself expresses no specific intent and it can only be supposed. The general intent of a grant or reservation of minerals by a fee owner was taken to be to create an estate in the mineral owner in the valuable substances usually removed from the ground by means of wells or mine-shafts but not by a method which would destroy or deplete the surface. The Court then declared that the following rule was “to be applied in determining whether an interest in the iron ore was conveyed by the deed” in that case:
Unless the contrary intention is affirmatively and fairly expressed, therefore, a grant or reservation of “minerals” or “mineral rights” should not be construed to include a substance that must be removed by methods that will, in effect, consume or deplete the surface estate.
The Court clearly based the disposition of Acker v. Guinn upon this rule and concluded that the conveyance of “all oil, gas and other minerals . . . that may be produced” included no interest in iron ore. The Court might have construed the conveyance to vest ownership of all ore in the mineral owner and allowed the problem of minerals lying near the surface to be met by limiting the implied easement of the mineral owner in the use of the surface for extraction or production of those minerals. That was not the holding in Acker v. Guinn. The substance which can be extracted only by substantial destruction of the surface is owned by the surface owner.
Here, as in Acker v. Guinn, the Court is construing a written instrument. If the instrument had specifically reserved coal and lignite, or if the conveyance had expressly reserved all minerals lying upon the surface or at any depth and including those minerals which may be produced by open pit or strip mining, the intention and effect of the instrument would have been clearly expressed. Furthermore, mineral ores and coal and lignite would ordinarily be reserved to the mineral interest owner by the terms of the Wylie to Baker instrument. That is not true, however, under Acker v. Guinn, if any part of the substance lies so near the surface that to be extracted it “must be removed by methods that will, in effect, consume or deplete the surface estate.” Because it is not expected that the parties to the instrument would have intended the destruction of the surface by the mineral owner in the absence of an expression of that intention, their use of “mineral” in the instrument is not construed to include the near surface substance. Once the instrument is construed to that effect, this particular substance — at whatever depth —is not a “mineral” for all purposes of the instrument.
Acker v. Guinn stands for the rule that a substance is not a “mineral” if substantial quantities of that substance lie so near the surface that the production will entail the stripping away and substantial destruction of the surface. That being the circumstance, and there being no contrary affirmative expression in the instrument, it controls the construction of the instrument as to the same substance at all depths.
It is improper therefore to declare that the surface owner is entitled to only so much of the substance as may be produced by strip mining or pit mining. We are not dividing the right to produce the substance; we are construing the instrument of conveyance to ascertain the ownership of the substance. Furthermore, the rule of construction does not favor the surface owner simply because it is shown that the substance “may” be produced by strip or pit mining. Instead, the surface estate owner must prove that, as of the date of the instrument being construed, if the substance near the surface had been extracted, that extraction would necessarily have consumed or depleted the land surface.
If the method of production required the removal of surface soil, it is immaterial that devices of restoration or reclamation were available. The thinking or intention or knowledge of the parties, or the lack of knowledge, would also be immaterial. The value of the substance, either on the date of the instrument or at any subsequent date, would not change the rule of construction announced in Acker v. Guinn.
*173 Disposition of Present Case
It cannot be said that the quoted reservation in the 1950 deed affirmatively and fairly expresses an intention to reserve to Wylie an interest in any substance to be found in deposits at the surface level of the land. Wylie argues that by describing “minerals on and under the land” the reservation evidences an intention to include minerals belonging to both the surface and to the sub-surface. We do not agree, because the preposition “on” has traditionally been used in conveyancing to mean more than “on the surface of.” See Anderson & Kerr Drilling Co. v. Bruhlmeyer, 134 Tex. 574, 136 S.W.2d 800, 805 (1940). It is suggested that there was shaft mining for lignite in this area of Texas prior to the date of the 1950 deed. This fact would have no effect if lignite were located at or near the surface of the land being conveyed and if in 1950 this shallow lignite would have been extracted only by a method that would have destroyed the surface of the land.
The record, however, does not prove the depth at which the lignite is located so as to show that the extraction of the lignite would have necessarily removed or destroyed the surface of the land. If lignite lies at the surface of the land, no further proof would be required to establish the title of Reed to the lignite as against Wylie’s claim under the 1950 reservation. Reed, however, presented only an affidavit of a landman for a utility company who stated therein that the coal and lignite will be removed from this land by open pit mining and that it can be recovered only by this method. If this is the expression of an opinion as to mining methods used for lignite mining at certain depths, no qualifications of the affiant are shown, and it has been held by this Court that expert opinion testimony does not establish the fact as a matter of law in support of a motion for summary judgment. Coward v. Gateway Nat. Bank of Beaumont, 525 S.W.2d 857 (Tex.1975); Gibbs v. General Motors Corp., 450 S.W.2d 827 (Tex.1970); Broussard v. Moon, 431 S.W.2d 534 (Tex.1968).
Movant Reed was not entitled to summary judgment. The Court of Civil Appeals judgment, remanding the cause to the trial court, is affirmed.
GREENHILL, C. J., concurring. DANIEL, J., dissenting, in which STEAKLEY, J., joins.